Applied Fitness Testing : An  Introduction 

Sports Injury

Body Composition

Muscular Strength

Blood Pressure & Heart Rate

Muscular Endurance

Lab & Field Tests

Flexibility

Aerobic Fitness

Muscular Power

Why Fitness Testing?

Introduction 

The aim of this page is to provide coaches and sports performers with a general insight into the role of fitness testing and how it may help them in their sport. It will also address some of the issues regarding what to be aware of when undertaking a fitness test and how to utilise the results. However, it is acknowledged that success in sport is not solely built upon physical fitness, but also requires good technical ability, mental skills and attitudes, all of which must be trained to meet the demands of the sport.

Why fitness test

Performance in any sporting event is the result of a multitude of factors, which include the amount of training performed, the body’s adaptation to the training, motivation level, nutritional status and weather conditions to name a few. As you can acknowledge, physiological parameters only account for a portion of any performance, and so the role of any exercise physiologist is also similarly limited.

Through fitness testing, the factors involving physiological processes, over which there is some control, can be measured and ultimately improved upon. Performance in any sporting event is the result of a multitude of factors, which include the amount of training performed, the body’s adaptation to the training, motivation level, nutritional status and weather conditions to name a few. As you can see, physiological parameters only account for a portion of any performance, and so the role of any exercise physiologist is also similarly limited. Through fitness testing, the factors involving physiological processes, over which there is some control, can be measured and ultimately improved upon.

Benefits of fitness testing 

Of the many benefits of fitness testing, the major use is to establish the strengths and weaknesses of the athlete. This is done by comparing test results to other athletes in the same training group, the same sport, or a similar population group. Previous test results of large groups are often published as normative tables. By comparing results to successful athletes in your sport, you can see the areas which need improvement, and the training programme can be modified accordingly. This way valuable training time can be used more efficiently. However, beware that some athletes perform well in their sport despite their physical or physiological attributes, and it may not be advantageous to be like them.

How can fitness testing help you?

Whether you are a coach or participant at club or international level, in whatever sport, fitness testing can almost certainly help your performance. The potential uses and benefits of fitness testing are the following. Evaluation of a performer’s strengths and weaknesses, relative to the demands of their sport. 

  • Aiding the prescription of suitable training loads.

  • Monitoring the effectiveness of training.

  • Providing short-term fitness goals.

 

What makes a good fitness test?

To provide useful information, fitness tests must fulfil certain criteria, which if not achieved could produce misleading information with undesirable consequences. Therefore fitness tests must be:

  • Sport specific/applicable

  • Valid

  • Reliable

  • Accurate

  • Sufficiently sensitive to detect changes in fitness

Test specificity / applicability

To be relevant to a sport, a fitness test must mimic one or a combination of the fitness demands

of that sport. For example, a treadmill would be used to assess a runner’s fitness, while a cycle ergometer would be used for a cyclist. Tests devised to assess team game sports performers should incorporate the types of movements and distances involved in that sport (e.g.

shuttle running). Whereas sports performers that utilise specific equipment may be required to wear.

Test validity

To be valid, a test must assess what it is intending to. For example, whilst completing as many press-ups as possible may be a good measure of muscular endurance, it is not a valid measure of maximal strength. Likewise, if a test lacks sport specificity it is unlikely to be a valid test for that particular sport. Poor validity may also arise if other factors have the potential to mask what is being assessed. For example, if assessing sprinting speed in hockey, it would be inappropriate to require the player to dribble a ball, as this would assess dribbling speed not sprinting speed.

Test reliability

Reliability refers to how repeatable and consistent a test is. Ideally if a performer repeated a test under exactly the same conditions with no change in their fitness they should produce identical results. However, in reality attaining exactly the same results are most unlikely due to slight differences by the performer from one day to the next. Coaches and performers should be aware that a relatively small change in the test scores may not mean a change in fitness.

 

Test accuracy

 

Test accuracy is incorporated into the test validity and reliability and covers the accuracy to which measurements can be recorded. For example, a highly skilled coach may be able to hand time with an accuracy of +/- 0.1 seconds, but would not be able to accurately record to +/- 0.01 seconds.

 

Test sensitivity

A test must be sufficiently sensitive to detect changes in fitness or else hard earned fitness gains could go undetected, which may severely de-motivate the performer and undermine the credibility of the coach. A test’s sensitivity will depend upon its reliability and measurement accuracy.

 

Types of fitness tests

 

Physical fitness is a complex, multifaceted phenomenon, composed of:

  • Aerobic power

  • Anaerobic power and anaerobic capacity

  • Muscular endurance

  • Muscular strength

  • Flexibility and joint mobility

  • Speed

For effective fitness testing the coach and performer need to identify the fitness components, which contribute to performing their sport, then select and administer an appropriate series of tests. For team and racquet sports, due to their complexity, this may require a detailed analysis of the sport. Since each sport differs in relation to the fitness components necessary, so the fitness tests used are also likely to differ.

Scientist on Computer
 
 
 

Body Composition

On the Scales

It is well recognised and documented that excessive body fat, particularly when sited centrally around the abdomen, is associated with hypertension, metabolic syndrome, Type 2 diabetes mellitus, stroke, cardiovascular disease), and dyslipidaemia. The Health Survey for England (2017) estimates that 28.7% of adults in England are obese and a further 35.6% are overweight. Obesity is generally defined as having a body mass index (BMI) of 30 or above. BMI between 25 and 30 is classified as ‘overweight’. The survey found that men are more likely than women to be overweight or obese (67.2% of men, 61.5% of women). Individuals aged between 65-74 are most likely to be overweight or obese. Unfortunately, the prevalence of obesity has progressively increased over the last three decades. More troubling are the statistics relating to children that estimates that 9.5% of children aged 4-5 are obese, with a further 12.8% overweight. At age 10-11, 20.1% are obese and 14.2% overweight. Children living in deprived areas in England are more likely to be obese. At age 4-5, 6.4% of those in the least deprived areas are obese, compared with 12.4% of those in the most deprived areas. At age 10-11, 13.3% of children in the least deprived areas are obese, compared with 26.7% in the most deprived areas. This gap has again increased over the last decade.

Essentially body composition can be expressed as the relative percentage of body mass that is fat and fat-free tissue using a two-compartment model. Body composition can be assessed with laboratory and field techniques that vary in terms of difficulty, cost, and accuracy (Duren et al., 2008 [Link]; Lee and Gallagher, 2008 [Link]). It is important to note that prior to collecting any data for body composition assessors or technician must be trained and experienced in the applied techniques. This may be via under the direct supervision initially of a qualified mentor in a controlled testing environment. In this section, different assessment techniques are summarised. It is beyond the scope of this section to provide information on every measurement and calculation estimates of body composition, body fat and fat three mass.

Anthropometrics Methods

Body Mass Index

BMI is easy to measure and calculate and is therefore the most frequently used tool to correlate risk of health problems with the weight at population level. It was originally developed by Adolphe Quetelet during the 19th century (termed Quetelet index [Eknoyan, 2007 [Link]). During the 1970s and based especially on the data and report from the Seven Countries study (Keys et al. 1984 [Link], researchers noticed that BMI appeared to be a good proxy for adiposity and overweight related problems.

 

BMI formerly known as the  Quetelet index is used to measure weight relative to height and is calculated by dividing body weight in kilograms by height in meters squared. For example, an adult who weighs 70 kg and whose height is 1.75 m will have a BMI of 22.9.

 

For most individuals, obesity-related health problems increase beyond a BMI of 25.0 kg.m-2. For adults that are overweight the BMI has been defined as 25.0-29.9 kg.m-2 and for obese individuals a BMI of  ≥ 30.0 kg.m-2 (Table 1). Unfortunately BMI fails to differentiate between body fat, muscle mass, or bone. However, an increased risk of hypertension, sleep apnea, Type 2 diabetes mellitus, certain cancers, CVD, and mortality are associated with a BMI ≥ 30.0 kg.m-2. When compared to individuals classified as obese, the association between a BMI of 25.0–29.9 kg.m-2) and higher mortality risk is uncertain. However, a BMI of 25.0–29.9 kg.m-2 is related to an increased risk of developing Type 2 diabetes mellitus, dyslipidaemia, hypertension, and certain cancers. A BMI of < 18.5 kg.m-2 also increases mortality risk and is accountable for the lower portion of the J-shaped curve when plotting risk on the y-axis and BMI on the x-axis (Flegal et al., 2005 [Link]). The use of specific BMI values to predict percent body fat and health risk (Gallagher et al.,  2000 [Link]). Because of the relatively large standard error of estimating percent body fat from BMI, other methods of body composition assessment should be applied to assess percent body fat during a physical fitness assessment.

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Table 1. Nutrition Status For adults over 20 years old

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Body circumference measurements

Diet Banana

Measuring individuals body circumference

 

The distribution of body fat distribution is acknowledged as an important indicator of health (de Koning et al. 2007 [Link]). Android obesity (i.e. the excessive distribution of abdominal fat on the midsection) increases the risk of hypertension, metabolic syndrome, Type 2 diabetes mellitus, dyslipidaemia, CVD, and premature death compared with individuals who more gynoid distributions (i.e., fat distribution on the hips and thighs) (Pi-Sunyer, 2004 [Link]). Furthermore, individuals who have increased abdominal fat are associated with a higher risk of developing metabolic syndrome.

 

Circumference (or limb girth) measurements may be applied to provide a general depiction of the individual’s body composition. This will be then assessed based on specific equations for both genders and age ranges (Tran and Weltman, 1988 [Link]; Tran and Weltman, 1988 [Link]). The accuracy is within 2.5%–4.0% range of the ‘real’ body composition if the client has similar characteristics to the original comparable population and the circumference measurements are accurate. A cloth tape measure with a spring-loaded handle is traditionally used to reduce skin compression and improve the reliability of measurement. Additional measurements are suggested at each site and should be obtained in a rotational order of all sites being assessed. The average of the two measures is used if they do not oscillate by more than 5 mm. Below contains the common measurement sites used to measure circumferences:

 

  • Abdomen

  • Arm

  • Buttock/ hips

  • Calf

  • Forearm

  • Hips/thigh

  • Mid-thigh

  • Waist

Waist-to-Hip Ratio

 

The waist-to-hip ratio (WHR) is the circumference of the waist (above the iliac crest) divided by the circumference of the hips and has traditionally been used as a simple method for assessing body fat distribution and identifying individuals with higher and more detrimental amounts of abdominal fat (Xavier and Pi-Sunyer, 2004 [Link]). Health risk increases as WHR proliferates, and this varies with age and sex. For example, Morris et al. (1993) produced a nomograph based on maximal exercise capacity and age for assessing a patients ability to perform a dynamic exercise to quantify the level of physical disability or relative capacity for physical activity. Based on the nomograph health risk is very high for young men when WHR is  0.95 and for young women when WHR is 0.86. Whereas individuals aged 60–69 years, have WHR cut-off value of >1.03 for men and >0.90 for women for the same high-risk classification as young adults (Morris et al. 1993 [Link]). Several methods for waist circumference measurement involving different anatomical sites are available. Evidence indicates that all currently available waist circumference measurement techniques are equally reliable and effective in identifying individuals at increased health risk (Ross et al. 2020 [Link])

Table 2. Risk Criteria for Waist Circumference in Adults

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Adapted from Alberti, Zimmet and Shaw (2006 [Link])

Supporting articles on body composition

  • Alberti, K.G.M.M., Zimmet, P. and Shaw, J., 2006. Metabolic syndrome—a new world‐wide definition. A consensus statement from the international diabetes federation. Diabetic medicine, 23(5), pp.469-480

 

  • Tran, Z.V. and Weltman, A. (1989) Generalized equation for predicting body density of women from girth measurements. Med Sci Sports Exerc, 21(1), pp.101-104.

 

  • Tran, Z.V. and Weltman, A., 1988. Predicting body composition of men from girth measurements. Human biology, pp.167-175.

  • Pi-Sunyer, F.X., 2004. The epidemiology of central fat distribution in relation to disease. Nutrition reviews, 62(suppl_2), pp.S120-S126.

 

  • Morris, C.K., Myers, J., Froelicher, V.F., Kawaguchi, T., Ueshima, K. and Hideg, A., 1993. Nomogram based on metabolic equivalents and age for assessing aerobic exercise capacity in men. Journal of the American College of Cardiology, 22(1), pp.175-182.

 

  • Ross, R., Neeland, I.J., Yamashita, S., Shai, I., Seidell, J., Magni, P., Santos, R.D., Arsenault, B., Cuevas, A., Hu, F.B. and Griffin, B.A., 2020. Waist circumference as a vital sign in clinical practice: a Consensus Statement from the IAS and ICCR Working Group on Visceral Obesity. Nature Reviews Endocrinology, pp.1-13.

Skinfold Measurements

 

Skinfold measurement is a procedure that estimates how much fat is on the body. It involves using a device called a calliper to lightly squeeze the skin and underlying fat in several sites. Body composition determined from skinfold thickness measurements correlates well (r = 0.70–0.90) with body composition determined by hydrodensitometry. The rationale behind skinfold measurements is that the amount of subcutaneous fat is proportional to the total amount of body fat. It is assumed that up to one-third of the individuals total fat is located subcutaneously. The proportion of subcutaneous to total fat according to Roche, (1996) varies with sex, age, and race. Therefore, regression equations used to convert sum of skinfolds to percent body fat should consider these variables to enhance test validity.

Table 3. Description of skinfold sites and procedures

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Adapted from ACSM (2014) Guidelines for Exercise Testing.

Skinfold assessment of body composition is highly dependent on the knowledge of the assessor, so knowledge of anatomical landmarks and practice of the technique is required to attain precise measurements. The accuracy of calculating percent body fat from skinfolds is approximately approximately 3.5%, assuming appropriate techniques and equations have been applied (Heyward and Wagner, 1996). Considerations that may led to measurement error within skinfold assessment include poor technique and/or an inexperienced assessor, an exceedingly obese or particularly lean individual, and an improperly attuned calliper (Heyward, 1998 [Link]).

 

Various regression equations have been established to predict body density or percent body fat from skinfold measurements (Table 4 and 5). A list of common equations that allow calculation of body density without a loss in prediction accuracy for a wide range of individuals (Heyward, 1998 [Link]; Jackson et al.1998 [Link]). Other equations have been published that are sex, age, race, fat, and sport specific.

Additional Digital Resources

Credit: ACEFitness How to Find Your Waist to Hip Ratio

Credit: La Tech: Seven site skinfold measurement (

Table 4. Male skinfold equations 

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Table 5. Female skinfold equations 

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Table 4 and 5. Adapted from from Jackson and Pollock (1985) [Link]

Densitometry

 

Body composition can be assessed from the measurement of an individuals whole-body density using the ratio of body mass to body volume. Densitometry has been frequently used as a criterion standard for evaluating body composition for several years. However, the restrictive issue in the measurement of body density is the accuracy of the body volume measurement as body mass is assessed as body weight. Body volume can be measured by hydrodensitometry (underwater) weighing and by plethysmography.

 

Hydrodensitometry (Underwater) and  Plethysmography Weighing

 

This method of evaluating body composition is founded on Archimedes’ principle that states when a body is immersed in water, it is buoyed by a counterforce equal to the weight of the water displaced (ACSM, 2014). This loss of weight in water allows for computation of body volume. Bone and muscle tissue are denser than water, whereas fat tissue is less dense. Consequently, an individual with more fat-free mass for the same total body mass weighs more in water and has a higher body density and lower percentage of body fat.

 

Body volume can also be measured by air rather than water displacement. One commercially available system uses a dual-chamber plethysmograph that measures body volume by alterations in pressure in a closed chamber. This equipment is now recognised and reduces the anxiety associated with the technique of hydrodensitometry.

Credit: GE Healthcare [bone density and body composition scan)

Credit: Utah State University [hydrostatic weighing]

Credit: Utah State University [Air displacement Plethysmography]

Other applied techniques

 

Other feasible body composition assessment techniques include dual-energy X-ray absorptiometry (DEXA) and total body electrical conductivity (TOBEC). Unfortunately, these systems have restricted applicability when testing within the health and fitness industry due to of financial cost and the need for highly trained personnel. Rather, the use of bioelectrical impedance analysis (BIA) are applied as assessment techniques in this setting.

 

Commonly, the accuracy of BIA is comparable to skinfolds if protocol adherence is ensured (e.g., assurance of normal hydration status), and the equations entered into the machine are valid for the specific populations being assessed. However, the capability of BIA to provide an accurate assessment of percent body fat in obese individuals may be limited due to differences in body water distribution compared to those who are in the normal weight range (Duren et al. 2008 [Link]).

 
 
 
 

Heart Rate and Blood Pressure

Image by Robina Weermeijer

The heart rate and blood pressure are two circulatory features that ensure that the supply of blood throughout the blood is appropriately maintained. The adjustment of blood supply alters depending on the physiological demands and the need for greater perfusion to the tissues. For example changes in body position [sitting to standing], exercise intensity, mode or type of exercise and the individual's psychological arousal may result in an adjustment of heart rate and blood pressure. Heart rate is often used as an indirect indicator of exercise intensity. It is used for monitoring, adjusting and individualising training programs. Chronic exercise training adaptations may also be monitored by the changes in individuals resting heart rate and also during exercise. The pressure in the arteries is in a constant state of flux and is continually being adjusted to meet demand. 

Heart Rate Control

A quick and easy method to assess cardiorespiratory function is to measure the individual's heart rate (HR). Typically at rest, the adult heart beats between 60-80 beats per minute. However, in well-trained adults or individuals on specific heart medication can result in lower resting heart rate values. Conversely, an increase in resting heart may be an indicator of poor cardiorespiratory function, overtraining, increases in stress and other negative factors.  

Assessing a clients HR must be performed under certain conditions. It is recommended the resting heart rate (RHR) be taken in the morning and on an empty stomach. This because during sleep and times of relaxation, the sympathetic nervous system is less stimulated, which allows the heart rate to better reflect the parasympathetic influence. The client should be placed in a distraction-free environment and seated. If the clients RHR is being monitored over time then the same environmental conditions should be replicated to ensure greater validity.  

During exercise, HR is a reliable indicator of the clients own exercise intensity and is used extensively to monitor cardiorespiratory function (Ehrman et al. 2009). The heart generates its pulse via the sinoatrial (SA) node which is located on the right ventricle. The SA nod is often known as the pacemaker of the heart. The heart is innervated by sympathetic and parasympathetic nerve fibres that originate from the medulla oblongata and the cardiorespiratory control centres within the central nervous system.  These fibres innervate the SA node with the atrioventricular (AV) node providing a tonic stimulus that can be either enhanced or depressed. The sympathetic nerve fibres increase heart rate and the parasympathetic nerve fibres slow the heartbeat down. 

The client's HR at rest is primarily influenced by the parasympathetic system. However, at the onset of exercise, the removal of parasympathetic influence initially allows the heart rate to increase to approximately 100 beats per minute. This is then followed by an increase in sympathetic activity that further accelerates HR on circulatory demands (Wilmore, Costill, and Kenney 2008).

Exercise Intensity and Heart Rate

Heart rate can be used as a non-invasive method to assess exercise intensity due to the strong correlation with exercise intensity and oxygen consumption (Adams and Beam 2008). Numerous cardiorespiratory fitness tests use exercise HR to estimate oxygen consumption by examining steady-state HR at a given workload (Franklin 2000). Steady-state HR  (SSHR) is indicated when the circulatory demands of the activity have been met by the circulatory system with no further increases in HR (Wilmore, Costill, and Kenney 2008). 

SSHR that ensues at any given absolute workload can alter significantly based on the individual's fitness level. For example, if a sedentary person and a highly trained person of similar size and stature were walking at four miles per hour (6.5 km/h), the sedentary person would have a much higher HR than the trained person, despite similar levels of oxygen consumption. This difference in efficiency is also reflected in the manner HR is adjusted between workloads. This is because an ineffective cardiorespiratory system relies on increases in HR more considerably to meet the demands of an increased workload. Ultimately, as exercise intensity increases, the sedentary person would approach maximal HR at a much lower workload compared to the trained person.   Additionally, after exercise has stopped, the trained person’s HR would return to normal more quickly than that of the sedentary person, providing another way HR can be used to predict cardiorespiratory efficiency. Given the relative ease of measuring HR, combined with the several ways HR can be used to predict cardiorespiratory efficiency, it is apparent why HR has been widely used.

Maximal Heart Rate

Maximal heart rate (MHR) is the maximum number of heartbeats per unit of time that can be achieved during an all-out effort to volitional exhaustion. MHR appears to decline with age and is often predicted by subtracting one’s age from 220 (Fox et al., 1974). This value is fittingly called an age-predicted maximal heart rate (APMHR). For example, a 50-year-old male would estimate his APMHR as follows: 220 – 50 (age) = 170. Although this method of estimating maximal HR can vary considerably among people and is only an estimate, it is used extensively as a field method to establish the upper limits of HR, without exposing individuals to the maximal effort required to measure a true maximal HR (Franklin 2000).

Heart Rate Reserve

Once APMHR has been computed, this data can be used to determine exercise intensity guidelines based on heart rate reserve (HRR) (Franklin 2000). This prediction formula includes one variable that is affected by age (APMHR or maximal HR) and one factor that is affected by the state of fitness (RHR). Determining RHR and APMHR permits the calculation of the number of beats the person can potentially use to meet the demands of exercise (i.e., beats held in reserve). Heart rate reserve is found by subtracting RHR from APMHR. Once the number of beats in reserve has been determined, a percentage of this reserve can be calculated by multiplying this number by the desired exercise intensity expressed as a percentage. By adding a percentage of the beats held in reserve onto RHR, a target HR can be determined to provide some objective criteria for monitoring training intensity. Both a minimum and a maximum training HR can be determined so that a desired training zone adaptation can be established.  

Worked Example 

First determining the age-predicted maximal heart rate by subtracting the clients age from 220 (APMHR = 220 – 22 [age] = 198 bpm). Next, subtract the resting heart rate from this number to determine the number of beats that are held in reserve (198 [APMHR] – 72 [RHR] = 126 bpm [HRR]). In this case, the individual needs a minimum of 72 beats per minute to meet the body’s demands at rest and 198 beats to exercise at maximal intensity. Therefore, 126 beats are held in reserve. These beats can be added to the resting heart rate to increase the circulation of blood as needed. 

For an individual wanting to train at approximately 70% of HRR, the calculation would look like this:

126 (HRR) × 0.70 (%) = 88.2 beats per minute

Target training HR = 72 (RHR) + 88.2 = 160 bpm ((70% of HRR)

Blood Pressure

Blood pressure (BP) is the force that the blood exerts on the walls of all the vessels within the cardiovascular system (Venes, 2009). The term blood pressure refers to the numerous variables that work concurrently to ensure the pressure required for blood circulation under a range of conditions (Guyton, 1991). These factors include the elasticity of the vessels, the resistance to flow before and after the capillaries, and the forceful contraction of the left ventricle, and the blood volume and viscosity (Smith and Kampine 1984). Blood pressure oscillates throughout the day depending on the metabolic demands, body position, arousal, diet, and other factors (Wilmore, Costill, and Kenney, 2008). Additionally, several hormonal, hemodynamic, and anatomical factors working together ensure the pressure needed for sufficient circulation of the blood.

 

As sport scientists or exercise professionals knowing the fundamental physiology of BP control and assessment is essential. As this is one of the basic vital signs used to appraise health, Blood pressure needs to be maintained within a certain range. At rest, normal systolic blood pressure is maintained between 100 and 120 mmHg, whereas diastolic blood pressure is maintained between 75 and 85 mmHg. Blood pressure that is constantly elevated (i.e., hypertension) can contribute to the development of the cardiovascular disease. If BP drops too low (i.e., hypotension), blood delivery can be compromised, which may lead to circulatory shock. During exercise and other strenuous activities, BP must be altered to transport larger amounts of blood and oxygen to the tissues. 

Hypertension

Hypertension is one of the most prevalent cardiovascular risk factors among Europeans (WHO 2018). This disorder is reasonably easy to identify but may go unnoticed primarily because symptoms are not evident to the average person. The primary cause of hypertension remains indefinable, yet the diagnosis and treatment of this condition are inexpensive. Therefore, routinely monitoring BP can be an effective screening tool to help those at risk before a major coronary event. The American Medical Association (Table..), indicates the various hypertension classifications for adults. It is important to note that BP tends to fluctuate throughout the day, hypertension may be incorrectly diagnosed or even undetected, based on the time and circumstances in which it has been assessed. To increase accuracy, individuals need to monitor BP at different times during the day, preferably under the circumstances of natural daily living. 

Table 6.  British Hypertension Society Classification of Hypertension

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Hypotension

Individuals that experience hypotension when the pressure in the system is compromised or insufficient to maintain the circulatory demand. Systolic pressure less than 90 mmHg, or a diastolic pressure of less than 60 mmHg, or both, normally indicates hypotension. This absence of pressure can leave the heart, brain, and muscles with insufficient blood flow. Hypotension can occur from dehydration associated with heat illness and other pathological conditions. Although much less common than hypertension, hypotension can be a very serious medical condition. The diagnosis of hypotension is highly individualised but is characterised by a significant drop in pressure from normal. Typically, signs of hypotension are dizziness, disorientation, or confusion. Other signs include blurry vision, fainting, and weakness. Hypotension may occur acutely with an orthostatic challenge and may also be caused by alcohol, certain medications, and a variety of medical conditions. Individuals who experience hypotension on a regular basis should endeavour to identify the exact trigger and seek medical attention if necessary.

Pressure Gradients and Blood Pressure

The movement of blood through the circulatory system depends on the development of pressure gradients (PG) (Venes, 2009). When blood is placed under pressure, it inevitably seeks an area of lower pressure. When an area of lower pressure is presented, the blood flows in that direction based on how great the difference is between the pressure of the current compartment, the pressure of the new environment, and the resistance to flow within the vessel. Within the arteries, capillaries, and veins, PGs must be generated to enable the movement of blood (Smith and Kampine 1984). Blood travels from the heart into the circulation based on the PG generated by the forceful contraction of the heart in relation to the pressure in the aorta. Initially, blood leaves the left ventricle of the heart and enters circulation under relatively high pressure as the heart rhythmically contracts and relaxes (Marieb and Hoehn, 2010). As the heartbeats, each cardiac cycle is comprised of a low-pressure filling phase (diastole), followed by a higher-pressure ejection phase (systole). Consequently, the volume of blood and the pressure of the blood that enters the aorta are continually fluctuating according to the cardiac cycle and the rhythmic design of PGs (Powers and Howley, 2007).

As the aorta and other large arteries receive this blood, they enlarge and store potential energy in the elastic fibres in the walls of the arteries and arterioles (Tanaka, DeSouza, and Seals, 1998). After systole has completed and the aortic valve closes, these vessels recoil and squeeze the blood, producing another PG that moves the blood to the vessels downstream. In each case, the blood moves down its PG pursuing an area of lower pressure while moving nearer to the capillaries where the exchange of gasses and nutrients can take place.

When the blood has entered the capillaries, the majority of the pressure produced from the heart has been dispersed, and the blood entering the venous side of the circulatory loop is under low pressure as it moves back to the heart (Wilmore, Costill, and Kenney 2008). To enable this blood flow in a low-pressure environment, the venous circulation is supported by three mechanisms that also create PGs. The first mechanism is the configuration of one-way valves located within the veins. These valves are arranged to promote unidirectional flow to combat gravity on the blood as it moves back to the heart. 

The skeletal muscles work in conjunction with the one-way valves by increasing intramuscular pressure within the active muscles. These muscle contractions create a PG by squeezing the blood in the veins of the muscles. Lastly, the respiratory system enables venous blood movement by generating a cyclic pressure difference within the thorax that corresponds to the rising and falling of the diaphragm. Both the skeletal muscle and respiratory pumps help “milk” the blood through the veins so that it returns to the heart under the influence of almost no pressure. PGs are essential for the movement of blood through the circulatory system. Anatomically, the human body is designed to circulate blood by creating PGs to facilitate blood movement (Marieb and Hoehn 2010).

Arterial Blood Pressure Regulation

Under resting conditions, the volume of blood on the arterial side of the circulatory loop is small (13%) compared with the volume contained in the capacitance vessels of the venous circulation (64%) (Wilmore, Costill, and Kenney 2008). At rest, this distribution of blood is sufficient to meet the pressure and circulatory demands of the body. However, when an increase in ABP is required, it can be achieved by assembling the blood from the venous side of the loop and redistributing it over to the arterial side (Powers and Howley 2007). Arterial blood pressure is dynamically changed by controlling the factors that regulate the volume of blood within the system. Arterial blood volume can be changed by increasing or decreasing cardiac output (Q), increasing or decreasing total peripheral resistance (TPR), or altering both factors concurrently.

Cardiac output is the total amount of blood that leaves the left ventricle each minute. It is computed by considering the stroke volume multiplied by the number of cardiac cycles (HR) completed in one minute. Total peripheral resistance represents the resistance the blood confronts while flowing from the arterial side of the cardiovascular loop over to the venous side. The relationship between the amount of blood entering the arterial circulation and the amount of blood permitted to leave finally determines whether ABP increases, decreases, or stays the same (Smith and Kampine 1984).

Acute Arterial Blood Pressure Regulation

The cardiovascular system is equipped with a negative feedback system that distinguishes ABP changes and reports them to the central nervous system, which response with alterations to blood pressure. These signals are sent to the central nervous system by specific pressure or stretch receptors termed baroreceptors (Marieb and Hoehn 2010). These receptors are strategically positioned in the aortic arch and carotid arteries, providing a tonic flow of information to cardiovascular centres within the medulla (Marieb and Hoehn 2010). Under low-pressure conditions, afferent input to the brain is decreased, and the brain responds by increasing and decreasing sympathetic and parasympathetic drive, respectively (Marieb and Hoehn 2010). Subsequently, HR and SV increase leading to increases in blood volume in the arterial circulation. A simultaneous increase in TPR prevents too much blood from exiting the arterial circuit, which eventually expands arterial blood volume and pressure. Under higher non-exertion-based pressure situations, adjustments are made in the opposing way.

Arterial Blood Pressure

Blood pressure fluctuates significantly in different segments of the cardiovascular loop. The term blood pressure is commonly used to denote arterial blood pressure (ABP), which is expressed in millimetres of mercury (mmHg). The arterial segment of the cardiovascular loop commences at the aorta and ends at the arterioles. Due to their elastic properties, these vessels can adjust to meet the dynamic pressure changes during systole and diastole. Arterial blood pressure is not a static pressure within the system, but a dynamic association between the upper and lower values attained between beats and over time. It is also important to understand that ABP is not representative of the pressure throughout all of the arteries, but a reflection of the pressure in the large arteries that are subject to the greatest degree of pressure change. Therefore, ABP is stated as two pressures. The highest pressure produced in the vessels during left ventricular contraction is denoted as the systolic blood pressure (SBP) and the lowest pressure ensues during the relaxation phase of the cardiac cycle called the diastolic blood pressure (DBP) (Pickering et al. 2005c). 

The numerical difference between SBP and DBP is termed pulse pressure (PP). At rest, an elevated PP may be used as an indicator of arterial compliance (Adams and Beam 2008). During exercise and other vigorous physical activities, it would be expected that PP rises as the need for additional flow are increased. Notionally, SBP is an indicator of the pressure of blood entering the arterial circulation, while DBP signifies the resistance of blood to leave. Therefore, if the difference between these pressures increases during exercise, more blood must be both entering and leaving the arterial circulation signifying a greater flow through the tissues.

Mean arterial pressure (MAP) can be calculated using SBP and DBP. Although ABP is always in transition within the arterial system, MAP represents the mean pressure in the arteries at any period. At rest, the pressure produced during systole denotes almost one-third of the entire cardiac cycle, whereas the diastolic phase is almost twice as long (Adams and Beam 2008). Therefore, the formula for computing resting MAP must account for the fact that the heart is in the diastolic relaxation phase for a longer period of time compared to the contraction phase. The formula for calculating the MAP at rest is as follows:

Resting MAP = 2/3 DBP + 1/3 SBP
Example: 120/80 (120 systolic and 80 diastolic)
80 DBP × 0.666 = 53 mmHg
120 SBP × 0.333 = 40 mmHg
MAP = 53.28 + 39.96 = 93 mmHg

During exercise, the diastolic phase of the cardiac cycle is reduced as the heart rate increases making the systolic and diastolic phases approximately equal. Consequently, the formula for MAP changes slightly to account for this change:

Exercise MAP = 1/2 DBP + 1/2 SBP
Example: 140/80 (140 systolic and 80 diastolic)
80 DBP × 0.50 = 40 mmHg
140 SBP × 0.50 = 70 mmHg
MAP = 40 + 70 = 110 mmHg


Exercise and Arterial Blood Pressure Regulation

When clients perform an acute bout of aerobic exercise, SBP normally increases to meet the metabolic demands of the tissues. DBP will feasibly stay the same, leading to an expansion of both MAP and PP. A release of the sympathetic neurotransmitters epinephrine and norepinephrine produces an increase in both HR and SV contributing to an expansion in arterial blood volume and finally ABP. This sympathetic response produces temporary vasoconstriction of the peripheral vessels permitting less blood to exit the arterial circulation compared to the amount flowing in from the increase in Q. These variables together temporarily expand arterial blood volume, increase ABP, and promote greater distribution of the blood to active tissues.

During acute bouts of intense anaerobic activity (e.g. resistance training), SBP normally increases substantially along with a concurrent increase in DBP. Pressures as high as 480/350 mmHg have been recorded during maximal lifts (MacDougall et al. 1985). For this reason, weight training has historically been contraindicated for many people with cardiovascular disease. However, the American Heart Association has now acknowledged the safety and potential value of strength training as a mode of therapeutic exercise if contemporary recommendations are followed.

The degree to which both SBP and DBP will be elevated may be related to the relative intensity of the exercise. During maximal or near-maximal lifting efforts, individuals often hold their breath, initiating the Valsalva manoeuvre. Although this tends to stabilise the midsection, it can also cause spikes in SBP and DBP (Sale et al. 1994; Sjøgaard and Saltin 1982). For this reason, people at risk for cardiovascular disease should avoid it.

Arterial Blood Pressure Measurement

Early approaches for measuring ABP used water columns to measure pressure, but these methods were large and significantly fluctuated on a beat-by-beat basis (Adams and Beam 2008). Finally, mercury columns were produced resulting in a more compact and manageable fluid column. Nowadays, ABP is commonly reported in millimetres of mercury (mmHg) regardless of the apparatus used for measuring. Despite their accuracy, sphygmomanometers that use mercury are vulnerable to breaking and exposing the mercury, which is a toxic substance and dangerous to humans. For this reason, many health professionals have replaced to automated BP cuffs or to aneroid devices. These devices are highly accurate if correctly calibrated.

A common technique using a sphygmomanometer can measure ABP at rest and during vigorous exercise (O’Brien, Beevers, and Lip 2001). Often referred to as the cuff method, this technique uses an inflatable tourniquet to temporarily occlude blood flow through the brachial artery. As the pressure is bled from the cuff, the medical professional listens to the artery below the cuff through a stethoscope and auscultates the various Korotkoff sounds (Table 7).

Arterial blood pressure can be measured using Korotkoff sounds based on how the blood flows through the brachial artery. Initially, the cuff is inflated to a pressure that prevents any blood flow through the artery. Because no blood is passing through the artery, no sounds or vibrations are detected beyond the cuff by the stethoscope. As the air pressure in the cuff is slowly released, the medical professional listens for the initial bolus of blood to pass through the previously closed artery. This first Korotkoff sound is indicative of SBP because the pressure in the artery must be higher than the pressure in the cuff if the blood in the artery has the PG needed to flow forward past the cuff through the semi- constructed artery.

As the cuff continues to be deflated, larger amounts of blood pass through the artery and the cuff during the systolic phase of each heartbeat. The classic lub-dub sound is heard while auscultating the heart directly. However, the sounds heard during blood pressure measurement are created by the blood that passes through the cuff when the pressure in the system exceeds the pressure in the bladder of the cuff. Because the cuff is still impeding some of the flow that would naturally pass through the brachial artery, vibrations can still be auscultated during this phase. Eventually, as the pressure in the cuff continues to fall, normal blood flow is restored. The pressure at which the restoration of normal blood flow and the concurrent disappearance of sound heard through the stethoscope occur is the DBP.

Table 7.  Korotkoff Sounds