Theoretical Models of Strength Training
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).
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).
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).
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.
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
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
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.
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.
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.
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.
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).
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.