Strength & Conditioning: An Introduction

Weight Lifting

Operational definitions and meaning of strength and resistance training


The terms ‘strength training’ and ‘resistance training’ have been frequently used to refer to forms of exercise with the primary goal of increasing muscular strength, hypertrophy or both (Fleck and Kraemer, 1998). However, the definition of ‘strength’ within physical conditioning professionals has not universally been agreed. This is because the term ‘strength’ has no explicit meaning (Rose and Rothstein, 1982). Fleck and Kraemer (1998) defined three concepts of strength; (1) static; (2) dynamic; and (3) explosive. Static muscular strength refers to strength assessed isometrically, dynamic strength as repeated efforts (several repetitions) until fatigue and explosive strength denoted as movements performed fast with maximal effort (Bandy, Lovelace-Chandler and McKitrick-Bandy, 1990). Other definitions of strength include the capacity of a muscle or groups of muscles to provide tension for maintaining postural control and initiating muscular movements during conditions of loading on the musculoskeletal system (Smidt and Rogers, 1982). According to Harman (1993) strength is the ability “to exert force under a given set of conditions defined by body position, the body movement type (concentric, eccentric, isometric, plyometric) and movement speed”. Therefore, we will define maximum muscular strength as the ability of a muscle or group of muscles to generate maximal force against an unyielding resistance in a single maximal contraction of unrestricted duration (Kroemer, 1972).

Early Origins

It is essential that academics and practitioners within the field of strength and conditioning and applied exercise physiology understand and appreciate the development of resistance training (RT) throughout history. As training practices that are currently prevalent are not novel; instead, they were performed historically, decreased in popularity, and returned within contemporary society. One may state that it is essential to understand the mechanics of the past to prepare for future developments, and it is vital to examine this facet of our training history. This chapter provides a historical account of the development of RT and discusses fundamental training theories that have aided in the design of contemporary RT recommendations.

The scientific literature on strength training (ST) is extensive; however, the leading training principles have not changed for centuries. Since the beginning of humanity, feats of strength have been documented from prehistoric drawings etched onto walls of caves, communicating how early humans survived by intelligence, strength, and agility. Resistance training has been applied by ancient Egyptians, Chinese, and Greeks (Todd, 1995). Egyptian hieroglyphics exhibited evidence of people lifting bags filled with sand and stone while performing swinging and throwing movements. Throughout China's warring state era (770-to-221 BC), initial tests of strength involved the lifting of ‘Qiao Guan’ (similar to a traditional barbell) and ‘Kang Ding’ (a three-legged meat cooking cauldron) (Stojiljković et al., 2013). In the ancient Greece era, the muscular development of the shoulders, back, torso, and arms were synonymous with masculinity and a healthy body, which evidence testifies from numerous statues and drawings saved from this era. The interest in muscular development was established long before contemporary bodybuilding competitions and other sports that required maximum strength and power (Stojiljković et al., 2013). Resistance exercise has also been part of the management of the patient’s health and wellbeing by physicians since Hippocrates in the armamentarium. Hippocrates described the importance of resistance training when he wrote: “that which is used develops, and that which is not used wastes away”.

Interestingly, a 143.5-kg block of sandstone, dated around the sixth century BC was lifted by an ancient Greek weightlifter named Bybon and is displayed in the Archaeological Museum of Olympia exhibit. The stone reads, “Bybon, son of Phola, has lifted me overhead with one hand” (Sweet, 1987). Though this seems dubious that a 143-kg block was lifted with only one hand above the head, it could be that Bybon lifted the stone with both hands and kept it held with one hand only. Similar stones were discovered in Asia, modern Greece, Palestine and Egypt. During the Roman Empire, gladiatorial training included many ST exercises that incorporated the ‘overload principle’ by severing wooden post with weapons much heavier than used in combat (Todd, 1995). However, with the demise of the Roman Empire, the philosophy of Christian austerity spread, and ST disappeared for 1000 years. In the 16th century, a continuing increase in physical activity was seen with ‘feats of strength’ starting to appear in the form of ‘strongman’ competitions that occurred during festive celebrations (Todd, 1995). The ‘strongman’ events created folklore heroes in almost every nation, with stories being passed down that recount’s deeds of human strength and heroism.

Early relationship with science and resistance training


As far back as Galen (129-to-199 AD), an association existed between the scientific community and the allure with muscular strength in humans. Galen, a prominent Greek physician, was thought to be the first medical doctor to recommend RT for health improvements. He endorsed the use of hand weights during gladiatorial training in which to condition the upper body and arm strength to aid with combat. During the Renaissance period (14th-to-17th century) further advancement was made with the prominent French writer Montaigne (1533-to-1592 AD) reporting the health benefits of RT when he observed his father’s physical condition (Kraemer and Häkkinen, 2006). Camerarius, a German educator, also reinforced the use of weight training for improved health and performance.  Within this period, there was also advancement in human anatomy and appreciation of the human musculoskeletal system. This was illustrated by the pioneering text of Vesalius (1514-to-1564 AD) ‘De Humani Corporis Fabrica’ and several works of Albinus (1697-to-1770 AD) who increased the understanding of human anatomy and, to some extent, the understanding of physical adaptations achieved through physical exercise (Kraemer and Häkkinen, 2006).

Nineteenth-century advancement


During the 19th and early 20th century popularity in RT increased and was seen across Europe and the United States with physical educators implementing ST philosophies from Germany and Sweden within a formal component of the school curriculum (Todd, 1995). These training programs were physically rigorous consisting of gymnastic and callisthenics exercise, with other modalities used including, flexibility exercises, sports and dance and manual resistance exercise. Intriguingly, the resistance equipment used within the curricula, such as ropes, medicine balls were similar to the equipment used in the ancient Greek era (Todd, 1995). Throughout this period, various individuals showed their physical strength while revealing to science the potential strength humans could possess. For example, a Harvard-trained medical doctor named George Baker Winship demonstrated feats of strength and promoted the ‘health lift’, mainly a partial deadlift movement (Kraemer and Häkkinen, 2006). Additionally, Dudley Sargent (1849-to-1924 AD) another Harvard-trained medical doctor designed several exercise machines and developed methods to assess muscular strength and performance (i.e. Sargent vertical jump test).

Nineteenth-century strongmen


During this era, several European ‘strongmen’ showed that RT could develop an individual’s strength and physical fitness while retaining an aesthetically pleasing physique.  These strongmen not only performed extraordinary feats of strength but also designed training equipment and physical movements that are still applied today. For example, the prominent Canadian strongman Louis Cyr (1863-to-1912 AD) performed a 310-kg back lift and was renowned for horse pull demonstrations. Another strongman was French circus performer named Louis Uni (1862-to-1928 AD) who trained with thick bars and completed one arm 80-to-90-kg snatch movements (Buck, 1998). Ludwig Durlacher (1844-to-1924 AD), a German strongman with extraordinary midsection strength claimed to have designed the Roman Chair. Another strongman and wrestler was George Hackenschmidt (1877-to-1968 AD) who later claimed to create the Hack Squat movement. With Henry Steinborn (1894-to-1989 AD) credited with designing the prototype for the modern-day Olympic barbell with rotating ends. Sigmund Klein (1902-to-1987 AD), a strongman from Germany who also showed high levels of physical fitness, also wrote many articles on weight training. During this period in Thomas Inch (1881-to-1963 AD) known as ‘Britain’s Strongest Youth’ and ‘Britain’s Strongest Man’ was famous for being the only person capable of performing a one-arm ground to an overhead movement with a 78.27-kg dumbbell with a handle diameter of approximately 2.5-inches. Several strength competitors frequently use the Thomas Inch Replica Dumbbell in training (Buck, 1998). Lastly, Eugen Sandow (1867-to-1925 AD), a German strongman, showed that individuals could be both strong and functionally muscular. Sandow is immortalised on the Mr Olympia bodybuilding trophy awarded to the winner of the contest each year (Todd, 2003).


However, during this time the anti-weight training community was critical, claiming that RT produced detrimental increases in muscle tissue that would diminish the individual’s movement and mobility. The anti-strength training community claimed that training with weights would cause individuals to perform muscle movements slowly and become less agile. Several ‘strongmen’ refuted these claims and attempted to dismiss these myths, with Arthur Saxon from the Ringling Brothers’ Circus proclaiming that weight training would improve individuals speed (Kraemer and Häkkinen, 2006). Unfortunately, despite the ‘strongmen’ disproving claims that RT results in unfavourable muscle growth, the anti-strength training community embedded the belief to the lay-person that RT was detrimental to physical health.

Twentieth-century advancement


Unfortunately, during the early-to-mid-19th century, many strongmen engaged in self-marketing for financial gain resulting in frequent misconceptions associated with RT and strength development (Table 1). Several strongmen also promoted various forms of training equipment and resistance programming, declaring that the apparatus and devised programs increased the individual’s strength without them becoming ‘muscle-bound’ (Todd, 2003). For example, Charles Atlas (Angelo Siciliano) promoted the alternative cable device while claiming that he started training as a 44-kg ‘weakling’ and developed into the worlds most perfectly developed man. His marketing and training philosophy, known as ‘Dynamic Tension’ comprised of a 15-minute per day workout consisting of 12-sessions of bodyweight and isometric exercises (Todd, 2003). By the 1920s, the marketing by Atlas led to several million-people incorporating some aspect of his training advice that still appears within health and fitness gymnasiums today. The RT literature became prevalent during this time and continued to rise in popularity, generating numerous training misconceptions concerning methods used to increase muscular strength.


Table 1. Publications on muscular strength development

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Twentieth-century advancement in science and resistance training


As ‘strongmen’ were demonstrating physical feats of human strength, scientific research was slowly attempting to understand the mechanisms behind muscular strength. These scientific endeavours to quantify methods that develop muscular strength have been studied as early as 1895 (Roux,1895). Initial physiological investigations sought to demonstrate and explain muscular strength development and functioning (Morpurgo, 1897; Siebert, 1928; Steinhaus, 1933; Donaldson, 1935; Donaldson and Meeser, 1935). Roux (1895) for example developed a procedure that could demonstrate that increases in muscle tissue are directly achieved by an increase in work effort over performing normal daily activities, and not by the repetition of accustomed daily effort for a longer duration. This premise of Roux (1895) lay dormant for 30 years until the work of Petow and Siebert (1925), Eyster (1927), and Siebert (1928) confirmed Roux original statement of the ‘overload principle’ when they established that muscular strength of rats increased when the running speed increased, not by the increased duration at the same speed. During this period, Morpurgo (1897) conducted a series of histological experiments that found that muscle fibres in trained dogs had a larger cross-sectional area compared to untrained dogs.


Regardless of the revival in ST, by World War II, the ST principles were not fully understood and were like those of ancient Greeks (Atha, 1981). Before the World War II era, most information regarding ST emerged in commercially skewed literature, with most of the evidence primarily ignored by the medical profession. However, following the war, DeLorme conducted a series of medical experiments that evaluated the use of ST in physical rehabilitation for orthopedically disabled veterans (Todd, 1996). Delorme, Schwab and Watkins (1948) emphasised that the use of heavy resistance loading and low repetitions would develop muscular strength and light loading with high repetitions would develop muscular endurance. Due to the increased physical recovery rates of patients that had completed ST, formal recognition was gained from the medical profession. Furthermore, DeLorme and Watkins (1951) published a book entitled ‘Progressive Resistance Exercise: Technic and Medical Application’ that provided a basic framework for RT prescription that provided descriptive terms and recommendations including the number of repetitions, sets, and frequency of training.

Historical Development of Resistance Training Guidelines Research

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Victorian-era Exercise machines (designed by Dr Gustav Zander)

Throughout the 1950s and 1960s studies began to manipulate and assess the effects of different RT variables (sets, repetitions, training frequency, loading, and inter-set recovery) which produced the basis for the current RT guidelines and recommendations on muscular strength development. Chi (1950), for example, continued from the excellent work of DeLorme but investigated the effects of RT on athletes, specifically examining the effect of RT on athletic power development. Chi demonstrated that RT produced more consistent increases in muscular power than when not engaging in an RT programme. During this period, Capen (1950) examined the effects of combining endurance and ST with athletic power development. Capen reported that the RT group demonstrated significant increases in strength and power development. Intriguingly, the RT group also significantly improved cardiovascular conditioning compared to the conditioning group.


In 1962, Berger conducted investigations into the optimum number of repetitions for one-set training. Each group trained with either one-set of two, four, six, eight, ten, or 12 repetitions. Berger concluded that less than two repetitions or more than ten repetitions would not improve bench press strength as quickly as four-to-eight repetitions when training one-set three days per week (d×wk-1). In 1963, Berger further investigated the effects of the training-dose with subjects performing either six-sets of two repetitions vs three-sets of six repetitions or three-sets of ten repetitions. Results from this study suggested that three-sets and six repetitions were more significant in improving bench press strength.  In 1965, Berger also investigated the effects of varied RT loading and strength development. Results from the study suggested that increases in strength may occur after two weeks of training two d×wk-1 at two-thirds of the 1RM, provided at least one maximum lift was performed one d×wk-1. In addition, training with a load of two-thirds or more of the 1RM for one-set, three d×wk-1 will not increase strength in six weeks. Berger concluded that the increase in strength was partially because of  the subjects performing 1RM one d×wk-1. This was further supported by the work of O’Shea (1966) and Withers (1970).


The study by O'Shea (1966) was similar in design to Berger, with subjects performing three-sets of five or six repetitions, three-sets of nine or ten repetitions, three-sets of two or three repetitions for six weeks. O'Shea reported no significant differences between treatment groups, with all three groups demonstrating increases in dynamic and static strength. A study by Withers (1970) compared the effects of subjects performing either five-sets of three repetitions, four-sets of five repetitions, or three-sets of seven repetitions for nine-weeks. Withers reported that all groups increased pre-to-post strength significantly but not between treatment group differences.

Theoretical models of strength training

The concept of planned training is not new, originating in ancient Greece and Rome (Drees, 1968) and has been written extensively in almost every RT textbook. Developing muscular strength is a complex process that involves systematically overloading the neuromuscular system and muscle cells initiating adaptational responses. Strength improvements are achieved because of a well-designed RT program that produces central nervous system and muscle cell adaptations. The current construct of the RT program for muscular strength has been developed [in part] from the pioneering work of DeLorme (1945) and DeLorme, Schwab and Watkins (1948) who developed the progressive resistance training hypothesis.


Over the last 70-years' theoretical models of training have evolved with studies attempting to simulate ‘real-world’ conditions. Training theory goes to significant lengths to explain the different time-points necessary that regulate stress and promote adaptational responses for strength development. A well-constructed RT program is established from the application of theoretical models and training principles that ensure recovery to stress. The significance of ensuring appropriate recovery periods that allow muscular adaptations has been documented (Haff, 2004a; Haff, 2004b). Stone and colleagues (2007) suggested three theoretical principles (General Adaptation Syndrome [GAS]; the Stimulus-Fatigue-Recovery-Adaptation Theory [SFRA] and the Fitness-Fatigue [Fit-Fat], reflect the recovery-adaptational response from RT. Each of these theoretical principles will be discussed in further detail below.


General Adaptation Syndrome


The physiological basis for planned and structured RT is to ensure that adequate recovery generates positive adaptational responses and is established from the initial findings of Selye. Selye, an endocrinologist, studied various types of biological stressors to organisms and developed the ‘General Adaptation Syndrome’ (GAS) hypothesis. Selye (1936) developed a conceptual framework that attempted to explain the relationship between stress and adaptation.  Selye (1936) suggested that there were biological responses to acute nonspecific nocuous agents (i.e. cold exposure, surgical injury, spinal shock, excessive muscular exercise and sublethal intoxication of drugs) on rats. Selye observed that a distinct syndrome appears which is independent of the damaging agent (e.g. excessive muscular exercise or drug type) and represents a response to the stressor.


Selye’s GAS model (Figure 1) suggests that when an organism is exposed to a stressor (i.e. RT), it will respond in three distinctive phases; (1) the alarm phase; (2) resistance phase; and (3) the exhaustion phase. For example, in RT, the alarm phase is because of the initial exposure to RT with the trainee’s body post-workout performing at a reduced capacity. This may be in the form of fatigue, stiffness, or delayed onset of muscle soreness due to stress exposure. The second phase (resistance to a stressor) is characterised by improved performance (super-compensation) as the body adapts and responds to the RT stressor. Finally, the third phase (exhaustion) is characterised by a reduction in performance as the magnitude or duration of the stressor is excessive with the body unable to adapt and respond.


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Figure 1. Selye’s General Adaptation Syndrome applied to resistance training and theory. For example, the individual is in a state of preparedness (homeostasis) and is represented by a straight line at the left of the figure (above). Note that during the resistance training session, the line shows that the individual fatigues, recovers, and then supercompensates (enters the resistance stage). If nothing else is performed, the individual returns to homeostasis via involution, or if continued to train without adequate recovery descends into overtraining and exhaustion due to the return of fatigue and the inability to continue to compensate for the applied stressors.


Stimulus-Fatigue-Recovery-Adaptation Theory


Verkhoshansky (1979; 1981) proposed the stimulus-fatigue-recovery-adaptation model (SFRA) suggesting that fatigue accumulates due to the strength and duration of a training stimulus (Figure 3). After individuals receive the stimulus from the training session, the body recovers dissipating fatigue and enables adaptation (super-compensation) to occur. Furthermore, Verkhoshansky’s SFRA model suggests that if the stress is not applied with sufficient training frequency, detraining will occur (involution). Stone and colleagues (2007) suggest that involution is also induced by the duration of the training program over the weekly training sessions. Equally, if no new training stimulus is provided after recovery and adaptation are completed, then involution will occur.


Further observations by Stone, Stone and Sands (2007) suggest that the magnitude of the training stimulus plays a vital role in determining the duration of the body’s recovery and regeneration period. For example, if the magnitude of the RT load is large, then a more considerable accumulation of fatigue will be produced, resulting in a more extended period of recovery (Stone, Stone and Stands, 2007). Equally, if the training load is reduced, less fatigue will accumulate, and the recovery-adaptation process will occur at a quicker rate. Therefore, alteration through the manipulation of training variables and sequencing of training workloads is essential for recovery-adaptation processes to occur. The management of training loading and workloads through a series of light and heavy training sessions can efficiently regulate fatigue and recovery while ensuring fitness levels are maintained or improved.

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Figure 3. The stimulus-fatigue-recovery-adaptation model suggests that fatigue accumulates in relation to the strength and duration of a stimulus. After a period of recovery, fatigue is dissipated, leading to super-compensation.

Fitness-Fatigue Model


The most prevalent stress-adaptational theory cited in training literature is the fitness-fatigue paradigm (Fit-Fat) (Bannister, 1982). This model partially explains the relationships among fitness, fatigue and preparedness (Figure 2.2) in response to the training sessions that affect the individual’s level of preparedness. Furthermore, it provides a comprehensive depiction of the physiological responses to a training stimulus. According to the Fit-Fat paradigm, individuals may be assessed based on the principle outcomes of training (i.e. fitness and fatigue).


The Fit-Fat hypothesis differs from the GAS and SFRA adaptational models, which assume that fitness and fatigue share a cause-and-effect relationship.  The Fit-Fat model, however, suggests that fitness and fatigue demonstrate an inverse relationship. For example, when training loading is the highest, fitness becomes raised; but due to the high training loads, an associated increase in fatigue occurs. This, therefore, suggests that strategies that maximise fitness and reduce fatigue will have the most significant potential to elevate an individual’s preparedness (Stone, Stone and Sands, 2007).

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Figure 4. The Fitness-Fatigue paradigm

It should also be noted that any training model is merely an interpretation of a real-world multifaceted process (Banister, 1991). Subsequently, a training model differs from the real-world but aims to replicate the most critical facets that need attention while disregarding aspects that are deemed unimportant. The Fit-Fat model represents the cumulative effects of training as one fatigue and one fitness curve. In the real-world, however, multiple fitness and fatigue after-effects possible occur in response to training that is interdependent and produces a collective effect. This may explain [in part] why there are varying individual responses to RT. When the three theories (GAS, SFRA, and Fit-Fat) are evaluated collectively, it is evident that there is a need to balance the development of physical fitness while aiding in the dissipation of fatigue. It, therefore, is essential that when designing RT interventions that the resulting training loading, patterns, and frequency be considered. This allows for the management of fatigue while maximising the recovery adaptation process. 

Physiological adaptations to resistance training

As discussed in the previous sections above, RT has a profound effect on various biological systems. Careful manipulation of acute RT program variables by strength and conditioning coaches and exercise practitioners can therefore promote positive alterations in muscular strength and hypertrophy. Therefore, it is essential to overview the main physiology mechanisms and adaptational responses that occur due to the RT stimuli. The modification or alteration to any RT program variable provokes a different RT stress stimulus and can lead to an increase or decrease in muscular strength (Figure 5). Therefore, an overview of three areas will be examined, namely: (1) the neurological adaptations to RT; (2) muscle adaptations; and (3) the endocrine responses to RT.

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Figure 5. Resistance training stress continuum and muscle adaptation. Within the parameters of training theory, three possible outcome pathways following resistance training stress.

Neurological adaptations to resistance training


Training for increased muscular strength not only affects muscle tissue but also results in changes in the central nervous system. Unfortunately, early evidence on neurological adaptations has been generated [in part] from indirect observations and inferences drawn from techniques that were applied to animal studies.  However, evidence over the last 20-years suggests that neural adaptations result from alterations in co-ordination and learning that aid in improved recruitment and activation of muscles during RT. This evidence has transpired due to non-invasive methods that capture electrical and twitch responses of muscle. 


Motor unit recruitment, rate coding, and synchronisation


Early observations on muscular strength reported that when performing a RT program, the muscle responds to the demands of increasing amounts of resistance lifted (Hellebrandt and Houtz, 1956).  This increase in muscle strength results from the ability of the nervous system to recruit motor units (MU) involved in the activation of the muscle and the adaptations at the muscle fibre (Sale, 1988; Tesch, 1988). These alterations in the nervous system following RT have been referred to in scientific literature as neural adaptations (Sale, 1988). Studies have reported increases in strength with no or minimal changes in the cross-sectional area of the muscle (Moritani and deVries, 1979; Tesch, 1988).


Motor unit recruitment


Henneman and Olson (1965) developed the selective recruitment theory, which states that MU’s are composed of the same fibre types and are innervated by motor neurons with different thresholds for each fibre type. The MU is considered the functional unit of the muscle and consists of a motor cell, the axon and terminal branches and all the individual muscle fibres supplied by the axon (Freund, 1983). A skeletal muscle, together with the motor neurons controlling it, comprises several hundred MU of different sizes (Figure 6). A single motor unit can innervate a few to several hundred muscle fibres with each specific muscle containing ten to several hundred MU. For example, muscles involved in eye movement have an innervation ratio of 1:4 (the number of motor axons divided by the total number of muscle fibres). Large muscles that do not require the same degree of motor control have an innervation ratio as large as 1:300 (i.e. gastrocnemius muscle) (Garnett et al., 1979). The force output of a muscle is determined by the sum of the force outputs of the active MU (Senn et al., 1997). An increase in force production is, therefore, a result of the systematic activation of a greater number of MU being recruited and an increased frequency of activation (rate coding) (Figure 7)

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Figure 6. Muscle innervation by the motor neurons. The ventral horn of the spinal cord contains motor neurons that innervate skeletal muscle fibres.

The size principle and the application to resistance training


The Henneman size principle states that when the central nervous system recruits MU for a specific activity, it initiates smaller, easily excited MU’s and proceeds to the larger more difficult to excite MU’s (Henneman et al., 1974). This orderly recruitment of MU provides a smooth graduation of force (Guyton, 1991). If the input to a pool of MU’s exceeds the excitation threshold of the motor neuron, the neuron will generate nerve impulses (action potential) to activate the innervated fibres (Guyton, 1991; Senn et al., 1997). Cope and Pinter (1995) specified that the motor neuron recruitment threshold is determined by the interaction between the strength and organisation of the synaptic inputs and motor neuron responses. Depending on the muscle, studies have suggested that maximal recruitment occurs between 30-to-90% of maximal voluntary contraction (Enoka and Fuglevand, 2001; DeLuca, Foley and Erim, 1996).  Linnamo et al., (2003) reported that the threshold for maximal recruitment was higher in static compared to dynamic muscle actions. Most peer-reviewed evidence suggests that there are no functionally significant violations of the size principle (Cope and Pinter, 1995).

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Figure 7. The size principle. Each circle denotes a motor unit made up of different types and numbers of fibres. The blue outlined circles are Type I motor units and the blue circles are Type II motor units, with larger circles depicting larger motor units containing more fibres. As one goes up the line of orderly recruitment, heavier and heavier resistances recruit more motor units and their associated muscle fibres. 

Until recently, the body of scientific evidence on neurological adaptations was derived indirectly with varied techniques used to evaluate neural adaptations. However, recent technological advancements have more accurately defined the specific neural mechanisms contributing to RT induced increases in maximal strength. Folland and Williams (2007) stated that neural adaptations are positive alterations in co-ordination and learning that enable better MU recruitment and activation of the muscles involved during a specific strength task. This is apparent, particularly in the early stages of when untrained individuals perform strength training, as there are disproportionately larger increases in muscle strength than muscle size (Figure 8).

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Figure 8. Neuromuscular interplay to resistance training stimulus over time.

However, there are several morphological and neurological factors that contribute to increased strength following RT.  Typically, increased size of an exercised muscle is regarded as the long-term adaptation, although this varies to the exposure to the training stimulus. The body of indirect evidence suggests substantial neurological adaptations may be due to learning and changes in the intermuscular co-ordination of agonist and antagonist interactions.  During the early stages of RT, strength is associated with greater neural adaptations (within several weeks). This is in contrast with trained and elite individuals as the extent of the adaptations are within the muscles, promoting an increase in muscle mass (hypertrophy) (Figure 9).

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Figure 9. Short-term to long-term neural and muscle adaptations to strength training.

Rate coding and synchronisation


As discussed previously, to activate and deactivate MU requires structured sequencing based on the size principle (Henneman et al., 1974). This sequence depends on the size of the MU with the smallest motor neurons recruited first and deactivated last, and MU with the largest motor neurons recruited last and deactivated first. According to Henneman and colleagues (1974), the order of MU recruitment is encoded by size and is not directly organised by the brain. The production of muscle force depends on the number of active MU and the rate at which the MU discharge action potentials. There are two kinds of rate coding with evidence suggesting that muscle force exerted during a voluntary contraction is dependent on the number of MU and the rates and frequency in which these MU discharge action potentials (Milner-Brown et al., 1973). These properties are known as recruitment and rate coding with early studies suggesting that recruitment is a more significant factor for low forces, whereas rate coding is more responsible for changes in muscle force at intermediate and high forces. Milner-Brown et al., (1973) introduced electromyography measurements that quantified MU synchronisation by measuring MU activity. This six-week resistance study indicated increased MU synchronisation in the first dorsal interosseous muscle of the hand. Milner-Brown, Stein and Lee (1975) performed a further cross-sectional study comparing weightlifters to a control group. Results from this study observed that all seven weightlifters showed a significant degree of synchronisation. Semmler and Nordstrom (1998) indicated that athletes possess greater MU synchronisation than untrained individuals with heavy RT, increasing synchronisation.

Muscle adaptations to resistance training

RT promotes structural and functional changes in the body as indirect observations made on the muscular size and strength of highly trained strength athletes. The magnitude of these muscular adaptations is directly proportional to the physical stress placed on the body (training volume, loading and frequency) and the recovery period necessary to produce favourable changes.


Muscle fibre types


Humans comprise of varying percentages of muscle fibres, with fibre composition varying between muscles and individuals (Gollnick and Matoba, 1984). Several classifications have been used to distinguish different fibre types established from biochemical, histochemical, and physiological evidence (Morris, 1969; Morris, 1970; Peter et al., 1972; Sale et al., 1983). Early researchers developed physiological techniques that assessed the contractile properties of muscle and the speed at which fibres can generate peak tension (Table 2). Two fibre types (slow-twitch [ST] and fast-twitch [FT]) were identified (Morris, 1969). These fibres developed different tension characteristics with ST developing tension more slowly than FT fibres but were resistant to fatigue. Morris (1969) reported that ST fibres are recruited for long term, low-intensity work and FT for short duration, high-intensity work (i.e. resistance training).


Early studies on RT programs demonstrated that FT and ST fibre ratio increased and selective hypertrophy of individual fibres following heavy progressive loading and explosive jump training (Thorstensson et al., 1976; Häkkinen Alen and Komi, 1985).  Thorstensson et al., (1976) examined the effects of progressive strength training on eight healthy male subjects (22-to-31 years) leg extensor muscles over eight-weeks. Thorstensson and colleagues reported that no or minor alterations were observed in anthropometrics, muscle enzyme, and fibre composition. However, the muscle fibre ratio suggested a specific effect of ST on fast-twitch muscle fibres. Häkkinen and colleagues (1985) examined 11 male subjects performing 24-weeks of high-load ST.  It was reported that subjects increased maximal isometric strength by 26.8%. The increases in strength correlated with significant increases in neural activation of the leg extensor muscles during an intensive period of training. Häkkinen et al., (1985) suggested that selective RT induced hypertrophy contributed to strength gain. Other researchers have also reported that heavy RT can influence hypertrophy on FT fibres, with Prince, Hikiia and Hagerman (1976) and Tesch et al., (1988) suggesting that weightlifting increases FT fibre area more than ST. Research suggests that resistance-trained athletes possess hypertrophied FT fibres, while endurance athletes have more hypertrophied ST fibres.


However, the development of staining techniques and electron microscopy measurements led to additional fibre classifications (Brooke and Kaiser, 1970; Burke et al., 1971). Researchers identified a third fibre type in addition to ST and FT fibres (Peter et al., 1972; Brooke and Kaiser, 1970; Burke et al., 1971). Rose and Rothstein (1982) combined the different classification schemes and described muscle fibres based on biochemical, histochemical, and physiological. The three muscle fibre types were reclassified:


  • Type I (slow oxidative, ST) fibres

  • Type IIA (fast oxidative glycolytic, FT-fatigue resistant) fibres

  • Type llB (fast glycolytic, FT-fast fatigable) fibres


Staron et al., (1984) applied this fibre type classification and performed a cross-sectional investigation on weightlifters, distance runners and sedentary individual’s fibre type ratios. The authors observed that weightlifters had a significantly larger type IIA area than the other two groups (distance runners [aerobically trained] and untrained [control] subjects).

Table 2. Overview of the evolution of identifying muscle fibre types.

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Muscle fibre adaptations to resistance training


As detailed previously the progressive overload of the muscle produced by the RT (stress) stimuli has been shown to increase the cross-sectional area (CSA) of the muscle (Håggmark, Jansson and Svane, 1978; MacDougall et al., 1977; Young et al., 1983). The relationship between increased CSA and strength gain have been demonstrated frequently within the scientific literature. However, the debate continues as to whether the CSA of the muscle is a result of hypertrophy (increased fibre size) or hyperplasia (increased number of fibres) (Figure 10).

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Figure 10. Hypertrophy versus hyperplasia.


Muscle hypertrophy


Muscle hypertrophy has been a frequently reported response to exposure to long-duration RT and is characterised by an increase in the individual muscle fibre diameter (Lüthi et al., 1986; Håggmark, Jansson and Svane, 1978; MacDougall et al., 1977; Young et al., 1983). Morpurgo (1887) first demonstrated that muscle fibres respond to an exercise stimulus by fibre enlargement without an increase in fibre number. Early studies performed pre-to-post strength measurements with subjects repeating strength testing to indirectly examine changes in measurable hypertrophy (Bowers, 1966; Coleman, 1969; deVries, 1968; Hellebrandt, Parrish and Houtz, 1947). Indirect evidence from dissection of rats suggested that the number of muscle fibres in skeletal muscle is permanent and that increases in muscle mass were the result of fibre hypertrophy not because of increased fibre number (Goldspink, 1970; Gollnick et al., 1981).

Evidence from human studies also supported the premise of changes to CSA because of RT. Delorme and Watkins (1948) proposed that increases in strength were due to motor learning and muscle hypertrophy. Moritani and deVries (1979) demonstrated that neural factors account for the greatest part of strength gains in the first three-to-five weeks in young untrained subjects. MacDougall et al., (1977) reported hypertrophy in human muscle after five months of RT. Håggmark, Jansson and Svane (1978) evaluated the CSA of weight lifters compared to sedentary subjects. Håggmark and colleagues observed that weightlifters had greater CSA compared to sedentary subjects, with the weightlifters having an increase in the size of the individual muscle fibre. MacDougall et al., (1984) examined the CSA of professional bodybuilders, intermediate bodybuilders and sedentary subject’s bicep brachii muscle. Using computerised tomography and muscle biopsy techniques, MacDougall and colleagues observed significantly greater CSA in both bodybuilding groups compared to sedentary subjects. However, no significant differences were reported between all three groups in the number of muscle fibres. The authors concluded that heavy RT increased the CSA of the muscle fibre and not the increased muscle fibre numbers. Longitudinal evidence by Lüthi et al., (1986) reported an 8.4% increase in CSA of the vastus lateralis muscle in humans after six-weeks heavy resistance training.


Muscle hyperplasia


Early RT research theorised that heavy RT might produce muscle fibre splitting (hyperplasia) in humans (Fleck, Deschenes and Kraemer, 1988). This hyperplasia hypothesis was supported by the observations made of longitudinal fibre splitting in the muscle fibres of rats (Edgerton, 1970), chickens (Sole and Christensen, 1984) and cats (Gonyea, Erickson and Bonde-Peterson, 1977; Gonyea and Erickson, 1980; Gonyea and Sale, 1983). The pioneering work of Gonyea and Erickson (1976) suggested that after maximal muscle hypertrophy was obtained additional strength development could only occur via the addition of new muscle fibres when existing muscle fibres are divided (Figure 2.8). 


Additional research performed during the 1980s studied the existence of hyperplasia in humans through cross-sectional studies comparing the muscle strength of athletes and bodybuilders with inactive subjects (Larson and Tesch, 1986; MacDougall et al., 1984). Both Larson and Tesch (1986) studies reported that hyperplasia was more evident in bodybuilders than sedentary individuals. MacDougall et al., (1984) further reported that bodybuilders did not have more muscle fibres than untrained subjects. Evidence of human muscle hyperplasia following RT is sparse. Moreover, research produced from animal studies has been criticised due to methodological errors associated with fibre number estimations from histological sections (Gollick et al., 1981). Most researchers agree that increased CSA of muscles following long term RT is primarily a result of muscle hypertrophy (Lüthi et al., 1986; Håggmark, Jansson and Svane, 1978; MacDougall et al., 1977; Young, Stokes and Round, 1983).

Endocrine systems response to resistance training

The endocrine environment has an essential influence on acute and long-term adaptational responses to RT (Häkkinen, 1989; Kraemer and Ratamess, 2004) (Figure 11). The human endocrine system adapts to the repeated stimulus of RT by increasing or decreasing hormone secretion depending upon the acute resistance training variables (ACSM, 2009). This is achieved by increasing or decreasing the number of circulating proteins that bind the hormone and protect it from degradation while rendering it biologically inactive and changing the number of cellular hormone receptors.

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Figure 11. Physiological and biochemical responses to resistance training in relation to muscular strength and hypertrophy.

The performance of RT stimulates anabolic hormonal responses, including Testosterone (T), Growth Hormone (GH) and Insulin Growth Factor one (IGF-1) but also a catabolic hormone (C) (ACSM, 2009). Stone et al., (1988) indicated that alteration to acute RT program variables dictates the extent of this hormonal response.  Training protocols (high set volume, moderate to high resistance load and short inter-set recovery) that recruit large muscle groups (i.e. squats, deadlifts, bench press) appear to produce the greatest endocrine response (Stone et al., 1988). Additionally, Staron et al., (1994) reported that changes in fibre type are due to hormonal adaptations in previously untrained men. Researchers have also observed that changes in muscular strength and power in competitive Olympic weightlifters have been correlated to chronic hormonal adaptations (Häkkinen et al., 1987; Fry et al., 2000).




T is a male anabolic sex hormone that is secreted from the Leydig cells of the testes under hypothalamic and pituitary-gonadal axis control (Viru and Viru, 2005). The primary role of T in RT is to promote protein synthesis of contractile proteins involved in muscle tissue, resulting in increased muscle mass and strength (Kraemer et al., 1993). Exercise can acutely increase or decrease circulating T and is conditional on the mode and intensity of exercise (Schmid et al., 1982). Increases in circulating T increases during relatively short, high-intensity activities (i.e. resistance exercise), while the decline in T is associated with increased duration including marathons and other ultra-running events (Kuoppasalmi et al., 1980; Schurmeyer et al., 1984).


Ahtiainen et al., (2003) reported that T plays an important factor in strength development with a relationship between changes in isometric strength and T. Intriguingly, Ahtiainen and colleagues also indicated that subjects who exhibited acute increases in T after training had a CSA increase of muscle more than those with lowered T. Spiering et al., (2008) reported that T causes an upregulation of androgen receptors with elevated muscle protein synthetic response for approximately 48-hours, although this period is reduced with training. The hormone response to RT has been frequently studied with the concept of endogenous T and androgen receptors interacting during the recovery period that stimulates protein synthesis, muscle hypertrophy and strength (Wilkinson et al., 2006; Crewther et al., 2009). This is further reinforced by Sinha-Hikim et al., (2002) who reported that when exogenous T (by supplementation) is combined with RT, significantly increases muscle mass and strength. However, a decrease in T may cause an increase in fat storage due to reduced fat oxidation, diminished resting energy expenditure, and increased adiposity (Zitzman and Nieschlag, 2003).

Growth Hormone


GH has been associated with the promotion of anabolism in both muscle and connective tissue. The anterior pituitary gland secretes GH polypeptides molecules from the acidophilic cells and enhances cellular amino acid uptake and protein synthesis in muscle, resulting in hypertrophy (Crist et al., 1991). The most frequently studied GH is the 22-kDa isoform molecule that consists of 191 amino acids with other isoforms functioning similarly in promoting tissue anabolism (Kimball, Farrell and Jefferson, 2002). Kraemer et al., (2017) suggest that a superfamily of different GH mediate biological actions during recovery to exercise stress and not merely the 22-kDa monomer. The GH receptor is abundant in various cells and tissues, and the understanding of recovery response patterns to RT is not fully understood (Kraemer et al., 2017).  The release of GH in the blood during recovery involves a multitude of GH that aggregate during recovery (Hymer et al., 2001).


Florini, Ewton and Coolican (1996) suggested that concentrations of GH in the blood depend on the specific exercise stimuli. RT has been shown to acutely elevate many GH variants and promote muscle anabolism (Spiering et al., 2008). Kraemer et al., (1993) indicated that post-exercise GH levels are elevated 30-minutes’ post-RT. However, the magnitude of GH level depends on the amount of muscle mass recruited, volume, intensity and rest periods (Kraemer et al., 1991; Gotshalk et al., 1997; Smilios et al., 2003). GH appears to be highly influenced by the volume of the RT protocol. A further study by Kraemer et al., (2010) suggested that short inter-set recovery periods and RT stimulate higher concentrations of immunoreactive GH in both men and women. However, alterations to the recovery period and increased resistance loading resulted in significantly lower levels of immunoreactive GH (Kramer et al., 2010).


Insulin-Like Growth Factor-1


IGF-1 (originally termed somatomedin C) is produced in many tissues, primarily the liver and is secreted in response to GH-stimulated somatic growth, and as a mediator of GH-independent anabolic responses in many cells and tissues (Fry, Kraemer and Ramsey., 1998). RT has been shown to increase concentrations of circulating and muscle IGF-1, although several studies have reported no change (Chandler et al., 1994; Bamman et al., 2001). Studies suggest that RT changes the concentration of IGF binding proteins that affect the biological activity of IGH-1 (Bamman et al., 2001; Nindle et al., 2000). In response to mechanical overload initiated by RT, mechanogrowth factor stimulates satellite cell activation with IGF-1 increasing the proliferation and differentiation of satellite cells that aid in muscle hypertrophy (Hather et al., (1991). 


Resistance training variables and the endocrine system


RT has been recognised as an effective method for strengthening muscles, connective tissue, and enhancing physical functioning associated with sporting performance. It is also acknowledged that these adaptive responses result from careful manipulation of acute training variables including load, volume, frequency, inter-set recovery, contraction velocity of movement, the range of motion, selection and order of exercise (ACSM, 2009). By altering the resistance volume and load affects several acute responses, including neural, hormonal, metabolic, and cardio-vascular responses (Häkkinen, Alen and Komi, 1985; Ratamess et al., 2007).


Manipulation of acute RT program variables stimulates anabolic hormonal responses including T, GH, and IGF-1, but also C (ACSM 2009). Typical strength and hypertrophy protocols (high volume, moderate to high resistance loading and short inter-set recovery periods) have been reported to produce the greatest endocrine response (Stone et al., 1988). Schoenfeld (2010) has suggested that increased RT volume stimulates extensive metabolic stress and mechanical tension that produces greater metabolite accumulation, substrate depletion and muscle damage (Figure 11). These factors activate anabolic responses during the recovery phase that leads to adaptational responses (Helms et al., 2015).


Subsequently, by controlling the RT volume and loading (altering the number of sets per exercise, the number of repetitions per set and the number of exercises per session) can affect metabolic and hormonal responses to RT (Borst et al., 2001; ACSM, 2009). For example, Willoughby et al., (1991) reported significantly greater GH and T responses with multiple-sets compared to one-set programs. Borst et al., (2001) observed that long term RT that uses multiple-sets per exercise is superior compared to single sets for strength development. However, it is unclear whether an RT dose-response exists between volume, loading, and RT adaptations. There have been reports of similar strength increases when two and four sets and two and three sets (Housh et al., 1992; Staron et al., 1994; Kraemer, 1997). In contrast, others have reported that three-sets were superior to two sets for strength development (Berger, 1962; Ostrowski et al., 1997).


Over recent years there have been several reviews and meta-analyses have examined the effects of set-volume and resistance loading on muscular strength and hypertrophy. This has generated varied debate and opinions on the optimal RT required to produce optimal strength gains. The use of higher set volume has been promoted in recommendations (ACSM, 2009; NSCA, 2008), review (Wernborn et al., 2007) and several meta-analyses (Rhea et al., 2003; Peterson et al., 2004; Wolfe et al., 2004; Peterson et al., 2005; Krieger, 2009). Unfortunately, the association between endocrine signalling and androgen receptor expression is (partially) elusive regarding strength and hypertrophic responses (Schroeder et al., 2013). However, it is essential to appreciate the fundamental role the endocrine system plays in muscle regeneration and adaptational responses.  Damas et al., (2016) reported that the increased magnitude of micro-damage to the muscles might be caused by either higher RT volume or loading, with myofibrillar synthesis associated with changes in muscle size. Equally, Ostrowski et al., (1997) reported that if RT volume is excessive, then it may limit optimal endocrine responses (T: C ratio). Ratamess and colleagues (2005) also observed that increased RT volume had been associated with a reduction in the number of androgen receptors, which may mediate muscular strength and hypertrophy development.

The aim of this section was to provide the reader with relevant evidence from early pioneering research (experimental and theoretical) that has shaped our current understanding regarding the underlying mechanism for muscular strength. The effects RT program design has on the adaptational responses of the neurological, muscular and endocrine systems towards muscular strength development. Evidence suggests that careful manipulation of acute RT program variables has a significant effect on neural adaptations, signalling pathways and hormone responses that may influence protein synthesis and therefore gradual protein accretion leading to increased muscle strength and size. RT appears to influence T, GH, and IGF-1 with studies reporting an association with favourable outcomes related to muscle strength. Most research concerning RT conforms to maximising hormonal responses to promote muscular strength and hypertrophy.


Consequently, examining muscular strength responses to manipulated RT variables (daily and weekly set-volume, loading and frequency) is necessary. The optimal stress response should, therefore, be determined relative to the volume of sets, loading and frequency for specific muscle groups. In practice, this information will aid in designing time-efficient strategies for RT to maximise muscular strength while improving training consistency and training compliance.


Section Two- Formation of Health & Fitness Organisation


Presently, resistance training is recommended for all individuals due to the potential to improve health, well-being and sporting performance in different population groups (clinical, fitness, and athletic groups) (ACSM, 2009). Since the 1970’s there has been a greater emphasis on the scientific study of resistance training. More recently there has been a shift in the perception of resistance training and the participation in this training mode.  Almost all athletes follow training programmes throughout the session and beyond (off-season, pre-season and in-season). This is due to the large volumes of scientific evidence that demonstrates the importance of training to enhance sports performance. This has created strength and conditioning coaching roles for all levels of competition (i.e. high school to professional levels). This increased popularity has provided opportunities for career development at various levels and settings. Paradoxically, limited advancement would have been made if it was not for the exploration in this area. 


Over the last few decades, scientific training principles have prevailed over pseudoscience and these principles are now fundamental in the development of valid RT prescription for different population ranges (Bird et al., 2005). RT is an exercise modality that is frequently recommended for different population groups (clinical, fitness and athlete) and it has been reported to improve physical health and well-being (ACSM, 2002; Kraemer, Ratamess and French, 2002). The associated health benefits for individuals performing RT cannot be underestimated. These benefits go beyond that of muscular strength and athletic performance, with the application towards muscular tension provided by RT alters and enhances an individual's well-being and longevity. 


The health benefits of RT are predominantly used as a preventative training modality or as a countermeasure to conditions where muscle weakness compromise an individual's functional capacity (muscle atrophy, sarcopenia, musculoskeletal disorders or injury). It is necessary to recognise that without the body's ability to contract muscles, we could not walk, lift, breathe, digest, or perform essential biological functions. A well-conditioned muscular system enables a physically active lifestyle and enhances health factors that may reduce the risk of degenerative diseases and medical complications (ACSM, 2009). Recent evidence has suggested that muscle mass index is a stronger predictor of life expectancy than body mass index and offers additional support to the importance of muscular strength and muscle mass (Srikanthan and Karlamangla, 2014). However, during the early 20th century, misconceptions surrounded RT with the belief that it was detrimental to physical health.

The development of scientific evidence on RT since the 1940s has progressively increased with a further upsurge in magnitude throughout the 1960s and 1970s. Researchers in the 1960s refined the seminal research performed by Delorme (1945) with systematic manipulation of different RT variables from longitudinal studies (Berger, 1962; Hellebrant and Houtz 1956; Berger, 1962; Berger 1965; Capen, 1950; O'Shea, 1966). This scientific evidence and promotion of RT helped transform the landscape with increased participation and understanding of the value of RT towards physical health and well-being. This upsurge in popularity since the early 1970s has now led to national health and fitness organisations recommending that this mode of exercise be incorporated into exercise programs. These organisations included the National Strength and Conditioning Association (NSCA), the American Heart Association (AHA), the American Association for Cardiovascular and Pulmonary Rehabilitation (AACPR), Cardiovascular and Pulmonary Rehabilitation and the American College of Chest Physicians (ACCP), and the American College of Sports Medicine (ACSM) all advocated the use of RT to increase physical health, performance and longevity.


The National Strength & Conditioning Association


Traditionally, strength athletes only performed resistance training (RT) to improve muscle strength, power, hypertrophy, and sports-specific fitness. Unfortunately, the strength programs were established specifically from the applied experiences of the trainer or coach. This generated an explosion of unsupported RT programs that created confusion for those that were prescribed it. Indeed, RT program design was initially more of an art than science, with trainers and coaches modifying the training dose based on restricted knowledge of the physiological responses to exercise. Fortunately, in the 1960s and 1970s, American football recognised the value in RT and hired strength coaches to improve performance. By the 1970s, most strength and power athletes were performing RT. A critical development during this time was the NSCA that spread RT recommendations and attempted to disperse misconceptions and started to distribute practical and scientific evidence throughout the different sports. By the 1980s, most athletes and their coaches embedded RT for almost all sports. From the conception of this professional body, there are now over 30,000 members in 72 countries.


The NSCA have released several books and training recommendations intended for athletic development rather than universal recommendations on RT. For example, Pearson et al., (2000) produced a series of basic guidelines for RT of athletes that allowed coaches to develop athletic performance safely. These recommendations were broader ranging, unlike other organisations with programming designed specifically to match the profile of the athlete and the sport. Unlike other generic training suggestions, the approach to loading and volume is periodised to avoid the potential of over-training syndrome. The NSCA recommendations are positioned around the stress-adaptational responses and sports performance.

The NSCA specified that RT programs for athletes should be developed based on the individual needs of the athlete and specific sport.  The NSCA, unlike other organisations, stated that RT programs should be developed from integrating of scientific knowledge while addressing the practical requirements of the sport. This is unlike other recommendations, as ultimately RT programming [in part] seeks to develop long-term adherence to the individualised program. This allows athletes to have programs that best meet their needs and the sport. Therefore, because of the sport, training approaches and programming draw on a broader range of knowledge and skills typically discussed in other recommendations. Strength trainers and coaches need to be creative while applying scientific knowledge to athletes’ specific needs, which is unlike the general population who have very linear goals (Kraemer, 2006).


The American Heart Association


In 1995, the Centres for Disease Control and Prevention and ACSM published a joint public health recommendation on Physical Activity and Public Health. These recommendations were provided to send a concise and clear public health message concerning sedentary lifestyles and the role physical activity can have on health improvements. These recommendations were supported and endorsed by the AHA, with healthy adults aged between 18-to-65 years encouraged as part of a physical activity routine to perform moderate-intensity aerobic (endurance) physical activity for a minimum of 30-minutes on five days each week or vigorous-intensity aerobic physical activity for a minimum of 20-minutes for three-days.


However, no recommendations were provided for individuals to engage in RT to improve health. In 2007, the updated recommendations included clarifications to the 1995 recommendations with muscle strengthen activities incorporated into the physical activity recommendations (Haskell et al., 2007). Healthy adults were recommended to perform eight-to-ten exercises (weight training, weight-bearing callisthenics) performed on two or more non-consecutive days each week using major muscle groups. For improvements in muscle strength, resistance loading of eight-to-12 repetitions of each exercise be performed until volitional fatigue was encouraged (Pollock et al., 2000).

The American Association for Cardiovascular and Pulmonary Rehabilitation


The AACVPR and the ACCP released a previous set of evidence-based guidelines in 1997 with the inclusion of physical activity to increase recovery. Since then, the ACCP and AACVPR released further recommendations with the addition of a strength training component to a program of pulmonary rehabilitation increases muscle strength and mass (Ries et al., 2007). However, no specific recommendations concerning the required RT dose were provided even though the evidence they produced supported inclusion within a structured exercise program.


The American College of Sports Medicine


The scientific community throughout the 1970s had a limited appreciation towards the benefits of RT towards improving population-level health, except for increasing muscular strength and endurance. Some researchers believed that these functional variables played a limited role in the general population’s health.  Indeed, ACSM (1978) initially produced exercise guidelines for population-level physical activity, stating that individuals need only perform aerobic exercise. This positional statement reflected the health and fitness trends and limited research on RT being performed during the 1970s. This evident lack of scientific research led to the exclusion of RT within exercise guidelines with greater importance placed on cardiorespiratory fitness and body composition. For example, epidemiological research during this period reported a strong relationship between aerobic endurance exercise and the prevention of cardiovascular disease (Fox and Skinner 1964, Kannel, 1970). This led to the significant promotion of aerobic activities to increase individuals V̇𝑂2max and was interpreted to improve physical health (Blair, LaMonte and Nichaman, 2004). Unfortunately, due to RT omission and increased promotion of aerobic exercise, some interpreted that RT was insignificant for improving physical health (Feigenbaum and Pollock, 1999).


In the early 1980s, RT was recognised as a method that could positively affect athletic performance. By the mid-1980s the medical community began to acknowledge the therapeutic value of RT on health-related aspects including low back health, weight management, bone health, and basal metabolic regulation (Feigenbaum and Pollock, 1999). The ACSM in 1990 included within its recommendations that an RT component should be incorporated within the exercise prescription for physical health and development. This acknowledgement of the therapeutic benefits of RT leads to other prominent organisations, including the AACPR, ACCP and AHA, to integrate RT within exercise programmes. This endorsement by other leading health and fitness organisations has helped to establish the ACSM as the main authoritative body of exercise prescription.


Currently, there are large volumes of published information and scientific data on RT with numerous recommendations on how to improve muscular strength across all age classifications that are founded on pre-existing literature (Table 3 and Figure 12). ACSM has published several position statements that provide recommendations for enhancing physical conditioning for specific population groups (novice to athletes). These recommendations include guidance on the resistance loading, training frequency, volume (sets x repetitions), exercise order, and exercise selection. Most novice trainees and newly qualified trainers are typically directed towards these ACSM position statements. These statements are made available via open access, and due to marketing, most individuals accept what has been published as scientifically correct and assume that the evidence has sufficiently filtered through the peer-review process. ACSM states that their guidance is the most authoritative, evidence-based statement issued by ACSM and often considered by some as definitive with suggestions that evidence is extrapolated from a large body of scientific data that provides a substantial burden of proof.


ACSM Position Statements & Training Recommendations 

The ACSM and other health and fitness organisations have provided statements on strength development from as early as 1990 through to the present recommendations. The physical activity recommendations for population-level health now acknowledge the benefits of RT to improve health-related factors including, improved bone density, functional capacity, basal metabolism and back health (Feigenbaum and Pollock 1999). Consequently, health-related recommendations began to include RT within an integrated physical activity program that also included aerobic and other forms of exercise (ACSM, 1990).


The ACSM from the early 1990s emerged as the only plausible organisation that attempted to provide RT recommendations for population-level health. For example, in the ACSM (1998) position statement, “The recommended quantity and quality for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults,” provided recommendations with RT included within the program design. These suggestions encouraged individuals to perform RT with one-set of eight-to-12 repetitions for eight-to-ten exercises, including one exercise for all major muscle groups, and 10-to-15 repetitions for older adults and the infirm (ACSM, 1998). This then leads to a series of recommendations that are diversified by population group and training objectives (ACSM, 2002 and 2009).

In 2002, ACSM produced a position statement that evolved from the previous 1998 statement. These new recommendations now included guidance for those healthy adults that wish to progress their muscular fitness. The purpose of this 2002 position statement was to increase guidance from beginner RT programs to progression models that can apply to novice, intermediate, and advanced trainees. The ACSM (2009) position statement further advanced training recommendations on strength development from previous recommendations. This was generated from further studies including reviews, epidemiological studies, clinical studies, and meta-analyses on various acute RT programme variables. These new recommendations stated that novice trainees perform one-to-three-sets for eight-to-12 repetitions with 60-to-70% 1RM loading and two-to-three-minute recovery. For intermediate trainees, multiple-sets for six-to-12 repetitions at 60-to-70% 1RM and two-to-three-minute recovery. Athletes were directed towards performing multiple-sets with varying repetitions at a loading of 80-to-100% 1RM with four-to-six-minute recovery, in which to avoid over-training.

Table 3. Development of standards, guidelines and position statements regarding strength training for adults

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Figure 12. Cited studies used to generate ACSM (2002) position statement and recommendations.

Barbell and Kettlebell Weights

Why do athletes and non-athletes resistance train


There are numerous benefits of performing resistance training, and individual’s train for different reasons including health and fitness-related goals. Most individuals engage in resistance training solely for recreational purposes where the overriding goals are to increase muscle size, improve endurance and to a lesser extent improve strength. Other individuals may have specific goals to enhance their muscular power, strength, size or endurance, whereas some engage in resistance training for rehabilitation. Rehabilitation suggests an individual has an injury or disease that has ensued which pose some physical constraint and now they engage in training to strengthen the weakened area. Furthermore, many individual’s perform prehabilitation where the primary goal is injury prevention ensuring muscles are balanced. Performance-based athletes engage in resistance training to increase athletic performance. During the competitive season, athletes engage in maintenance training, ensuring that off-season gains and adaptations are maintained as best as possible within the competition. The training modality shifts towards more sports specific conditioning, practice, and competition. This phase is temporary until the competitive season is concluded.

Maintenance training is not solely reserved to athletes and many non-athletes may participate in this training depending on their circumstance. Many non-athletes engage in resistance training to elicit positive health adaptations to their body (i.e. muscle, nerve, skeletal and cardiorespiratory systems). Finally, individuals do not have to explicitly need to train for one goal; rather, many individuals train with multiple goals. This is often referred to as integrative training where multiple goals are pursued training purposes. 

Benefits of resistance training


There are numerous benefits of performing resistance training, and individual’s train for different reasons including health and fitness-related goals. Most individuals engage in resistance training solely for recreational purposes where the overriding goals are to increase muscle size, improve endurance and to a lesser extent improve strength. Other individuals may have specific goals to enhance their muscular power, strength, size or endurance, whereas some engage in resistance training for rehabilitation. Rehabilitation suggests an individual has an injury or disease that has ensued which pose some physical constraint and now they engage in training to strengthen the weakened area. Furthermore, many individual’s perform prehabilitation where the primary goal is injury prevention ensuring muscles are balanced. Performance-based athletes engage in resistance training to increase athletic performance. During the competitive season, athletes engage in maintenance training, ensuring that off-season gains and adaptations are maintained as best as possible within the competition. The training modality shifts towards more sports specific conditioning, practice, and competition. This phase is temporary until the competitive season is concluded.

Maintenance training is not solely reserved to athletes and many non-athletes may participate in this training depending on their circumstance. Many non-athletes engage in resistance training to elicit positive health adaptations to their body (i.e. muscle, nerve, skeletal and cardiorespiratory systems). Finally, individuals do not have to explicitly need to train for one goal; rather, many individuals train with multiple goals. This is often referred to as integrative training where multiple goals are pursued training purposes. 

As indicated earlier there are numerous health and performance benefits of resistance training (Table 4). Several studies have demonstrated the positive effects resistance training has on improving multiple aspects of an individuals health and sporting performance. Collectively, these studies have been performed on a range of population groups ( clinical, older adults, children and athletes), and it has been suggested that resistance training is a safe and effective mode of exercise for most individuals. These ramifications are critical to enhancing the performance of activities of daily living and optimal athletic performance. 

Table 4. Benefits of Resistance Training.

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Components of fitness


Health-related fitness components


Strength and conditioning programs focus on developing multiple levels of individuals physical fitness. Fahey and colleagues (2005) stated that fitness components can be divided into two areas (i) health-related and (ii) skill-related fitness components. Health-related fitness components are those that are considered to improve health, wellness and quality of life. These improvements to various systems can enhance physical performance and include muscular strength, muscular endurance, cardiorespiratory endurance, flexibility, and body composition.

Muscular strength


Muscular strength has been defined by Hoffman (2006) as the maximal force an individual can generate during a specific movement pattern at a specified velocity of muscular contraction. To assess dynamic muscle actions, a one-repetition maximum lift (1RM) is performed by the individual for a given exercise (i.e. squat, deadlift, or bench press) normally in a weights room or gymnasium. The trainee would move the maximal amount of weight they could lift in one all-out effort. However, depending on the population group it may be estimated from submaximal strength performance. The all-out effort (termed maximal magnitude of force) may be defined as absolute muscular strength as it represents the threshold of an individual’s physiological capacity for a specific resistance exercise. When maximal strength is expressed in relation to an individuals body mass, it is defined as relative muscular strength. For many, relative muscular strength is critical when athletes compete in different weight classifications because of the higher strength-to-mass ratio. Athletes with a higher strength-to-mass ratio enable high levels of force production without the addition of considerable mass gains. Relative strength measures have been used to compare lifting performances among athletes of different sizes. In lifting competitions (powerlifting), the Wilks and Sinclair formulas have been used and are established on the athlete's body mass to find a conversion factor that is multiplied by the weight lifted to correct for size differences.

Muscular endurance

Muscular endurance is the ability to maintain performance and resist fatigue. It is important to note that the intensity of muscle contractions plays a critical role. Submaximal muscular contractions are characterised by the ability to sustain low-intensity (low loading) muscular contractions for a prolonged period. Strength endurance is the ability to maintain high-intensity muscular contractions over a prolonged period. For example, an athlete can perform repeated sprints with comparable times or the athlete performs a certain number of repetitions for a resistance exercise over several sets despite a rest interval in between sets. Another term often used is local muscular endurance. Local muscular endurance is defined by the ability of specific (local) muscle or muscle groups to sustain the performance of that exercise. Generally, having good muscular endurance is important for body posture, health, and injury prevention and aids in improving athletic performance.

Cardiorespiratory endurance


Cardiorespiratory endurance is the ability to perform sustained aerobic exercise at moderate to high intensities. Cardiorespiratory endurance is correlated to the function of the lungs, heart, and circulatory system, and the capability of the muscles to extract oxygen and thus maintain performance. The central measure of cardiorespiratory endurance (sometimes termed aerobic capacity) is the maximal oxygen uptake (Vo2max). A moderate-to-high Vo2max is an essential component for endurance athletes, and having a good aerobic foundation can increase recovery from anaerobic exercise. Cardiorespiratory endurance is necessary for optimal health whilst reducing risk factors for disease, improving self-image, cognitive functioning, and mental health management.



Flexibility is the ability of a joint to move freely its ROM (see stretch training physiology for a detailed explanation). Improved joint flexibility can help reduce injury risk, improve muscle balance, increase physical performance, improve body posture, and reduce the occurrence of low back pain. To increase flexibility individuals should perform exercises in a full ROM and participate in an appropriate stretching program, preferably at the end of the session.

Body composition

Body composition refers to the amount of fat and fat-free mass (lean body mass) throughout the body. Lean body mass consists of bone, muscle, water, and other non-fat tissues. Healthy body composition involves the reduction of the fat component while maintaining or increasing the lean body mass component. An individual with a disproportionately high amount of body fat may be considered obese and is at an elevated risk of disease. The most effective way to improve body composition is to consume food at the correct qualities and ratios (i.e. low saturated fat intake, low simple sugar consumption, moderate protein intake, and appropriate kilocalorie intake) and regular exercise. Resistance exercises (i.e. strength training) and other modes of anaerobic exercise (high-intensity interval training [HIIT]) are effective for improving body composition as it increases lean body mass. Body composition is central to athletes who’s sports have weight classifications (boxing, wrestling and Olympic lifting) or where athletes have to overcome their own body mass (high jump, long jump, gymnastics or even endurance sports). 


Skill-related components of fitness

Skill-related components of physical fitness include power, speed, agility, balance and coordination, and reaction time. These components may be improved by a variety of different training approaches including resistance training, interval training, agility and plyometric training and through a series of sport-specific practices. 


Power is the rate of performing work. It is important to note that power is the product of force and velocity, thus there is a strength component to power development (strength at low-to-high velocities of muscular contraction). Starting strength is a term used to describe power production during the initial segment of the movement. Rate of force development describes power output during explosive exercise activity. The velocity component of the power equation indicates that high contraction velocities (or at least the intent to contract at maximal velocities even against a heavy resistance) of muscle contraction are essential. Therefore, power development is multidimensional, involving the development of force and velocity components. Muscle power may be improved by resistance training, speed, agility, and plyometric training, and through sport-specific conditioning.


Speed is an essential component of the sport. Speed is the capacity of an individual to perform a motor skill as quickly as possible. For example, linear running speed may be defined by three distinct segments: (i) acceleration, (ii) maximum speed, and (iii) deceleration. The acceleration phase is characterised by an increase in speed and is conditional upon strength, power, and the individual's reaction time. The maximum speed phase is characterised by the individual’s ability to maintain their maximum speed (e.g. speed endurance). The deceleration phase is, therefore, a result of fatigue and is characterised by involuntarily decreasing the speed after maximum speed has been achieved. Speed may be improved by a combination of training methods including non-assisted and assisted sprint training, strength and power training, plyometrics, technique training, and sport-specific practice.


Agility is the ability to change direction quickly without a substantial loss of speed, balance, or bodily control. To be agile requires muscular power, strength, balance, coordination, speed, anticipation, and neuromuscular control. Agility is an essential component of any sport that requires changes of direction, decelerations, and accelerations. Agility training involves predetermined drills (closed drills) and drills that develop the athlete's anticipation skills in which they react explosively (open drills). Likewise, agility can be improved by plyometrics, multidirectional agility and reactive drills, strength and power training, balance training, and sport-specific training.

Balance and coordination

Balance is the ability of an individual to maintain their equilibrium. It involves control over the individuals centre of gravity (often referred to as the centre of mass)  and allows them to maintain correct body position during complex motor skill performance. Balance can be improved by strength and power training, plyometrics, sprint and agility training, specific balance training (with unstable equipment), and through sport-specific practice. Gross motor coordination refers to the ability of an individual to perform a motor skill with correct technique and accuracy. Critical components of coordination include balance, spatial awareness, timing, and motor learning. 


Section Three - Principles Of Training & Conditioning

CrossFit Equipment
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Figure 13. Resistance training programme design considerations for muscular strength, with the incorporation of acute programme variables and fundamental training principles.

Over the last 60 years, greater awareness has been given towards the therapeutic effects resistance training has on muscular functioning and physical health. Scientific exploration and investigation into physical training practices have resulted in improvements in strength, hypertrophy, and muscular endurance. However, within the weight training and athletic communities, pseudoscience has often been the primary catalyst that drives unsupported recommendations for strength development. Besides, commercial gyms provide trainees with misinformation regarding the construct of a training programme. Unsubstantiated advice is often provided to these trainees regarding what acute programme variables should be modified (i.e. repetitions, set configurations, resistance loading, inter-set recovery periods, and training frequency) that would help to develop muscular strength. As a result of this misrepresentation of evidence, the development of training guidelines has evolved from pseudoscience that guides the lay-person. Fortunately, contemporary exercise physiology now ensures that greater emphasis is placed on empirical evidence that focuses on the manipulation of RT variables and the application towards strength development. Current scientific literature has advanced the development of RT programmes from the early work of the 20th century. However, the evidence on the effects of manipulating RT variables has on muscular strength is still sparse. Current RT methods and guidelines have been established without a substantial body of scientific evidence that can support these assertions.


Essential principles and programme variables of resistance training prescription


RT has grown in popularity over the last 35 years, with resistance exercise being practised as a recreational activity and to enhance athletic performance. This mode of exercise is prescribed (in part) by physicians, coaches, and exercise professionals with the premise of improving individuals’ general level of health and fitness. It has also been suggested that RT is an appropriate method to improve physiological health including increased bone density (Menkes et al., 1993), reduce pain and discomfort from arthritis (Rall et al., 1996), decrease low back pain (Nelson et al., 1995), improve glucose metabolism (Hurley, 1994), and counteract obesity (Heyward, 1998) when integrated within an exercise programme. There has also been a body of scientific evidence that has demonstrated that RT is an effective method that improves neuromuscular functioning and is applicable in the development of individual health status (Baechle and Earle, 2008). These health benefits of RT are primarily a preventative countermeasure where muscle weakness compromises optimal functioning. Resistance programmes are also used as a method that enhances athletic conditioning and performance and aids in the rehabilitation of sporting injuries (Behm and Colado, 2012).


The effectiveness of an RT programme depends on the careful manipulation of training variables in which to develop maximum strength (Figure 13). However, trainees of various levels and experiences expect to develop muscular strength by following generic RT programmes that are often generalised training principles. These programmes are based upon established scientific training principles and are often interpreted as the fundamental basis of developing muscular strength. Unfortunately, these training principles only serve as a starting point and provide information that applies to general health development. That said, a well-designed RT programme that is regularly performed can produce numerous benefits, including increased muscle strength, size, and alterations to body composition (Baechle and Earle, 2008). However, designing an RT programme that improves muscular strength is a complex process that incorporates several acute training programme variables and fundamental training principles (Figure 13).













Progressive Overload


Trainees must be exposed to an overload stimulus at regular time-periods to induce strength training adaptations. Overload represents the magnitude of work required to disrupt the biological equilibrium and generate an adaptational response. RT, therefore, imposes physiological stress that disturbs the homeostatic equilibrium (Brooks et al., 2005). Acute bouts of RT result in transient physiological and metabolic changes, which then return to pre-exercise levels during the recovery period. However, if resistance exercise sessions are repeated over a prolonged period, they may induce chronic adaptations. RT can result in altered metabolism (Coyle, 2000), changes in neuromuscular recruitment patterns and remodelling of tissue (Häkkinen et al., 2003). For strength progression to occur, the physiological system must be disturbed. This overload stimulus can be manipulated by altering acute training variables (Bompa, 1999). These acute training variables include set-volume, loading, inter-set recovery, frequency, and selection and order of exercise (Bird, Tarpenning and Marino, 2005).

Progressive overload refers to the gradual increase in physiological stress placed on the human body during physical training (Hoffman and Ratamess, 2008). As already discussed earlier the concept of progressive overload is not original and dates back several thousand years ago to the ancient Greek strongman and Olympic wrestling champion Milo of Crotona (Figure 14). Importantly, the human body has no aspiration to become physically stronger or conditioned unless it is required to meet higher physical demands. The lack of progressive overload in a program is a prominent factor for inert development. The use of progressive overload can overcome accommodation. Accommodation is the staleness resulting from the limited adjustment in the training program (Zatsiorsky and Kraemer, 2006). Adaptations to a training program take place within a few weeks of administering. Correct manipulation of acute program variables, therefore, alters the imposed training stimulus, and if the stimulus exceeds the individual’s conditioning threshold, then further improvements in muscular fitness can occur. 


Manipulation of resistance training variables

Progressive overload can be integrated into any resistance training in various means. These can include: 

  • The loading that is limited may be increased. For example, the individual may train with a higher relative percentage of their 1RM or use greater absolute loading within a continual repetition structure. For example, during weeks the initial training sessions (weeks 1-to-3) the individual trains at 70% of 1RM for several structural exercises. During weeks 4-to-5, the loading is increased by 5% to 75% of their 1RM, with a further increased in loading occurring at weeks 6-to-8 (80% 1RM).

  • Other overload considerations are including additional repetitions. For example, individuals performing repetitions between 8-to-12RM loading range where the individual performs a set number of repetitions for an exercise. During week 1 and 2 of training, the individual lifts 100kg in the bench press for 3 sets of 8 reps. During weeks 3 and 4, the loading at 100kg is maintained but performs 3 sets of 10 reps. During weeks 5 and 6, the repetitions are further increased to 12 for 3 sets with 100kg. Once 3 sets of 12 repetitions are achieved over two consecutive sessions, the individuals increase loading and perform 8 reps and repeat the sequence.

  • Coaches and trainers may also increase the lifting velocity with submaximal loads to increase the neural response. The intent of the individual to lift the weight as fast as possible is necessary. Because force = mass x acceleration, increasing repetition velocity (while the mass remains constant) results in higher peak force and greater strength improvement.

  • Modifications of individuals inter-set recovery periods may enable greater loading. If considered in combination with the above approaches, increasing the rest interval will enable greater recovery between sets allowing individuals to tolerate heavier loading. 

  • Session and weekly training volume may be also be increased within reasonable limits (2%–5%) or varied to accommodate heavier loads (Fleck and Kraemer, 2004). From novice to intermediate training, small increases in volume have been reported to increase hypertrophy. However, some evidence suggests with further progression it is the modification of both volume and intensity that becomes critical in program design.


  • Other training approaches have been suggested at supramaximal-loading training ranges. For example, methods such as forced repetitions, heavy negatives, partial repetitions in the strongest area of the range of motion (ROM), and variable-resistance devices have been used to load either a section of the ROM or a muscle action with greater than 100% of 1RM. It is recommended that these techniques should be used cautiously and only by experienced individuals.


Currently, there is limited and contradictory evidence that guides academics and fitness professionals on the effects of modifying RT variables and maximal strength development. Information is limited regarding the effects RT has on different population groups (trained, untrained, healthy adults, and older adults) and exercise selection (multi-joint and single-joint exercise). It is essential to consider that the application of different training principles and types of RT modalities can produce significant increases in strength or muscle hypertrophy if the correct ‘exercise-dose’ is applied. If each resistance exercise training session creates enough training stimulus to stress the specific muscle or muscle groups, a training effect occurs.


To achieve maximal results in muscular strength development, one must consider the science that has helped plan the appropriate programme structure and design. Kraemer and Ratamess (2004) state that “the act of resistance training, itself, does not ensure optimal gains in muscle strength and performance”. There have been several questions that have been proposed concerning the appropriate RT prescription that are intended to produce functional changes in muscular strength (Hass, Feigenbaum and Franklin, 2001. Currently, there is debate regarding which RT modality most effectively increases maximum strength. For example, studies have been performed on the mode of exercise (Cotterman et al., 2005), order of RT exercise (Simão et al., 2005), training frequency (Di Brezzo, Fort and Hoyt III, 2002), inter-set recovery (Henselmans and Schoenfeld, 2014), and daily training volume on strength training (Schoenfeld et al., 2016). However, of all the different RT factors, training volume, set-volume and resistance loading have received the most scientific attention.

Training specificity

The principle of training specificity requires that all training adaptations are specific to the stimulus being applied. Although in many situations general phycological improvements take place, most adaptations will be due to the specific stimuli. Training adaptations are specific to the muscle actions involved, the velocity of movement and rate of force development, range of motion, muscle groups involved, energy metabolism, movement pattern, and loading/volume of training (Kraemer and Ratamess, 2004). Specificity becomes most apparent when individuals progress to more advanced resistance training modes with several studies reporting that training effects in untrained and moderately trained individuals.

This training effect applies to:

  • Strength residue from unilateral training (to the opposite limb).    

  • Strength residue from the trained muscle action to a untrained action

  • Strength residue from limited-ROM training to other areas of the ROM or full ROM.

  • Strength residue from one velocity to another. 

  • Motor performance (jumping ability, sprint speed, and sport-specific movements) improvements resulting from resistance training.


To keep the training stimulus optimal the training variables must be modified over time. This is to create an environment that the human body has to constantly respond to and is, therefore, critical for adaptations to take place. Fleck (1994) reports that there is a large body of scientific evidence that supports the promotion of systematically varying training volume and intensity in comparison to programs that did not adopt this approach. Training sessions may be altered in a variety of ways and coaches and trainers should seek to develop a ‘toolbox’ which provides them with an array of strategies for creating progression. It is also important to understand that there is a minimum of 50 modifications that can be made to a training stimulus and as such the coach or trainer would benefit to be aware of program design variations (Figure 15).

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Figure 14. Milo of Crotona and progressive overload

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Figure 15. Programme design of resistance exercise for specific training outcomes incorporates the acute programme variables and key training principles btn = between; CON = concentric; ECC = eccentric; ex = exercise; ISO = isometric; RM = repetition maximum.  Adapted from Bird et al, (2015).

Training status


The training condition or status of an individual has a profound affect on the pattern of progression form a specific fitness component. It is important to understand that the training status reflects the process of adaptation that has occurred over a period of time. Considerations should be made regarding the individuals fitness level, training experience, and their genetics as these factors significantly contribute towards training progression. For example, untrained individuals have the largest rates of improvement as there is the greatest window of adaptational responses. Whereas highly resistance trained individuals demonstrate a slower rate of progression. The ACSM (2002, 2009) position stand specified a diminishing return in strength gains as the individual progressed from untrained to elite.


•  40% increase in untrained individuals strength

• 20% increase in moderately trained individuals strength

• 16% increase in trained individuals strength

• 10% increase in advanced individuals strength

• 2% increase in elite athletes strength

The training condition or status of an individual has a profound effect on the pattern of progression from a specific fitness component. It is important to understand that the training status reflects the process of adaptation that has occurred over a period of time. Considerations should be made regarding the individual's fitness level, training experience, and their genetics as these factors significantly contribute to training progression. For example, untrained individuals have the largest rates of improvement as there is the greatest window of adaptational responses. Whereas highly resistance-trained individuals demonstrate a slower rate of progression. The ACSM (2002, 2009) position stand specified a diminishing return in strength gains as the individual progressed from untrained to elite. 

  • 40% increase in untrained individuals strength•

  • 20% increase in moderately trained individuals strength

  • 16% increase in trained individuals strength

  • 10% increase in advanced individuals strength

  • 2% increase in elite athletes strength

Unfortunately, it is very difficult to accurately classify individuals into training categories as some individuals with several years experience posses less strength than some wit limited experience and vice versa. Even though the evidence is generated from short and longitudinal studies, the training methodology and testing procedures vary greatly between studies. From an observational perspective, one can see that progression becomes increasingly difficult as the individuals conditioning improves. A meta-analysis by Rhea et al. (2003)  reported that untrained individuals generally respond more positively in training progression than observed in trained individuals. Importantly most evidence has been derived from strength-based studies, however, it may be inferred that the responses may be similar to other fitness variables. Regarding progression made in strength, progression evidence suggests that with each improvement brings the individual closer to their genetic limits.  Early evidence from Hickson et al., (1994) demonstrates that the majority of strength increases within the initial weeks of a training program (weeks 1-to-4). After this period the rate and the magnitude of strength progression decrease as the individuals have higher levels of conditioning. This then creates plateaus in progression as the individual is closer to their genetic potential and further adaptation generally is more difficult to improve (principle of diminishing returns). Coaches and trainers need to ensure that all training programs carefully consider and incorporate progressive overload, training specificity, and variation to augment progression.


Detraining (Reversibility) 

Detraining is the complete termination or substantial reduction in training frequency, volume or intensity that results in a reduction in performance and the loss of specific physiological adaptations associated with training. The duration of the detraining phase and the training status of each individual will dictate the degree of performance losses. For some trained athletes these performance reductions may occur within the first two weeks. Studies have demonstrated that in recreationally trained males, muscle strength can be reduced within four to six weeks of detraining (Kraemer et al., 2002; Terzis et al., 2008). Izquierdo et al. (200&) reported that trained individuals had a greater reduction in power than strength after a period of detraining. Evidence has implied that this strength reduction initially is related to neural mechanisms then as detraining progresses changes to the cross-sectional area of muscle (atrophy) (Terzis et al., 2008) and reduced enzyme activity (glycogen concentration reduction by 40%) and anaerobic substrate concentrations (Creatine phosphate reduction by 25%)  (MacDougall et al., 1977). However, the muscle strength levels even after a period of detraining are seldom lower than pre-training levels which suggest training has a residual effect when cessation occurs. Interestingly, a study by Staron and colleagues (1991) founded that when individuals return to training the magnitude of strength acquisition is high.