Aerobic Testing Theory
In order to move the body forward (walking, running), turn pedals (cycling), lift the body against gravity (stepping) or overcome the resistance of the water (swimming, rowing), the body must perform ‘work.’ However, to sustain biological work the body requires chemical energy in the form of adenosine triphosphate (ATP). ATP is derived from the metabolism of carbohydrate, fats and proteins and requires oxygen for continual synthesis. Unfortunately, the body cannot store oxygen.
Via the cardiorespiratory system oxygen is breathed in and transported to working muscles to be used for energy production. During exercise more work is performed, and more work means more energy is needed, thus increasing the demand for oxygen. Eventually a point is reached where the cardiorespiratory system cannot supply enough oxygen to meet the increased energy needs. A point of ‘maximum oxygen uptake’ has been reached and is universally expressed as VO2 max (ml∙kg-1∙min-1). Functionally, VO2 max reflects the ability of the lungs, heart, blood and vascular system to transport oxygen and the ability of the tissues to extract and use oxygen (Laukkanen et al., 2002). A person’s VO2 max is a good indicator of how aerobically fit they are. In other words, an aerobically fit adult will be better able to take in, transport and utilise oxygen compared to unfit individuals.
Compared to unfit individuals, aerobically trained adults also live longer and enjoy a better quality of life (Blair et al., 2001, Vita et al., 1998, Wang et al., 2002). Since, no other fitness component offers the same benefits, it is important that aerobic fitness is measured by the personal trainer (PT). It is also important to assess aerobic fitness because most adults are considerably less fit than they believe (Allied Dunbar National Fitness Survey, 1992). Furthermore, the health benefits of exercise cannot be stored: protection from disease requires a lifelong commitment to aerobic exercise (Paffenbarger et al., 1978).
Cardiorespiratory fitness and VO2 max are influenced by gender, age, heredity and the dose (frequency x intensity x duration) of exercise training. Although there are high and low-responders, vigorous exercise has been shown to increase VO2 max by around 20% in sedentary individuals, regardless of age, gender, race and initial fitness level (Skinner et al., 2001). For these reasons, it has been concluded that the level of aerobic fitness that is needed for reducing the risk of disease is not limited by the genetic make-up of most individuals (Laukkanen et al., 2002).
Work rate v oxygen uptake:A relationship exists between work rate and VO2. Increasing the work rate increases the oxygen requirement; double the work rate and you double the requirement for oxygen. The highest amount of oxygen that can be taken in, transported and utilised is termed VO2 max, and is equal to maximum heart rate (MHR). For example, a fit versus an unfit persons oxygen requirements are the same at any given work rate. In other words, the same amount of energy is required for an unfit and fit client to run at the same speed, hence the same amount of oxygen requirement. However, unfit persons will reach their VO2 max sooner, therefore, having limited ability to sustain higher exercise intensities.
Work rate v heart rate:
During higher exercise intensities, greater demand is placed on the cardiovascular system to deliver oxygen to working muscles. Once again a relationship exists between heart rate and exercise intensity. As exercise intensity increases, heart rate rises, and does so in a linear fashion up to a point. It is generally accepted, that as fitness improves the heart rate will fall for any given work rate. This drop in heart rate is due to central and peripheral cardiorespiratory adaptations. Generally speaking, a person’s MHR remains unchanged, although, in elite endurance athletes the MHR may actually lower due to central cardiovascular training adaptations.
Heart rate is often used to evaluate exercise intensity. Commonly used methods include:
- heart rate method:
max heart rate (MHR) = 220 – age
The MHR method does not take into account the great variation between one individual to another which may lead to errors in prescribing exercise intensity (+/- 11 beats).
- heart rate reserve method:
HRR = MHR – resting heart rate (RHR)
Training heart rate (THR) = HRR x (50 to 85%) + RHR
The HRR method is a better correlation to a persons VO2 max, therefore, a more accurate method for prescribing exercise intensity.Both methods are more accurate when true MHR has been determined.
Work rate v lactic acid (metabolic thresholds):
During all intensities of exercise, aerobic and anaerobic mechanisms contribute varyingly to ATP synthesis. As exercise intensity increases, aerobic metabolism is supplemented by anaerobic ATP synthesis with the accumulation of lactic acid.
In a laboratory, blood lactate concentration can be monitored to identify metabolic changes that occur during exercise of increasing intensity, and can be used to identify a number of important thresholds. The aerobic threshold (AeT) is identified by a sustained increase in blood lactate concentration above resting levels. This threshold marks the transition from aerobic metabolism to metabolism that is both aerobic and anaerobic. Exercise below the AeT is comfortable, sustainable and ideal for recovery or long-duration work. Exercise beyond the AeT can for some individuals be demanding, but enhances performance by taxing aerobic respiratory mechanisms and improving one’s ability to dispose of lactate.
Whilst the accumulation of lactic acid in the contracting muscles probably does not cause fatigue (Nielsen et al., 2001), its accumulation in the blood causes an intolerable increase in acidity (pH). During exercise, the body attempts to buffer lactic acid by combining it with bicarbonate to produce carbonic acid, a weaker acid that dissociates in the lungs to water and exhalable carbon dioxide (CO2):
Lactic acid + bicarbonate à carbonic acidDuring low- and moderate-intensity exercise, breathing is sufficient to expel CO2 and buffer blood lactate. As exercise intensity increases, however, a threshold exists beyond which the increase in blood pH stimulates a dramatic reflex-mediated increase in breathing (as the body attempts to expel excess CO2). This threshold is known as the ventilatory or anaerobic threshold (Cooper and Storer, 2001), as shown in the diagram below. The anaerobic threshold (AnT) is the intensity associated with a rapid rise in blood lactate concentration. The so-called ‘maximal steady state’ that exists at the AnT indicates that exercise beyond this level is not sustainable (Levine, 2001). However, exercise beyond the anaerobic threshold is ideal for interval training. It is noteworthy that, in the general population, the anaerobic threshold occurs between 40–85% of VO2 max and must, therefore, be identified for each individual (Jones and Ehrsam, 1982). As fitness improves the point at which lactic acid rises, occurs at higher workloads.
Metabolic Thresholds and Rating of Perceived Exertion (RPE)
Although metabolic thresholds cannot be identified outside the laboratory, there is a remarkably consistent relationship between metabolic thresholds and rating of perceived exertion. Exercise at the AeT is perceived as ‘light’ (RPE = 11), whilst exercise at the AnT is perceived as ‘somewhat hard’ to ‘hard’ (RPE = 13–15) (Prusaczyk et al., 1992; Demello et al., 1987; Mahon et al., 1997). What’s more, the ability of RPE to identify the AnT is independent of mode of exercise, gender and training status (Hetzler et al., 1991; Demello et al., 1987).
The relationship between RPE and metabolic thresholds allows the fitness professional to identify training zones using RPE data obtained in an exercise test (Zones 1-4). New clients should be tested to identify the exercise intensity associated with an RPE of 11–12 (Zone 2). After two to three months of regular training, a second exercise test should reveal substantial improvements in fitness, as indicated by lower heart rates at each level. The goal now is to increase exercise intensity without unduly taxing the client. Intermediate exercisers will not tolerate exercise beyond the AnT, and an RPE of 13–15 is appropriate at this stage (Zone 3).
Intermediate to advanced status is probably best facilitated by interval training. Interval training (zone 4-5) is characterised by bouts of high-intensity exercise interspersed with lower-intensity recovery periods. To prescribe interval training ‘in the field,’ the fitness professional again turns to RPE data obtained from regular exercise tests.
Beyond the AnT, lactate starts to accumulate rapidly. RPE is strongly influenced by blood lactate, consistently producing scores of 16–17 at concentrations ≥4 mmol/l (Seip et al., 1991). Initially, intervals at RPE 16–17 won’t be tolerated for more than one or two minutes. With training, however, these work periods will lengthen at the expense of recovery periods. The table below demonstrates the physiological correlation between the different zones and methods of monitoring and prescribing intensty.
|Zone||Upper limit||Physiological correlates|
|2||Aerobic threshold (AeT)||Sustained increase above resting level||60-75||50-65||11–12|
|3||Anaerobic threshold (AnT)||Rapid rise||75-90||65-85||13–15|
|4||Anaerobic 1||≥4 mmol/l||80-95||80-95||16–17|
Aerobic Test Protocols
The direct measurement of VO2 max requires trained personnel, expensive equipment and is rarely practical outside the laboratory. However, aerobic capacity can be assessed using a number of indirect tests. Furthermore, there is a relationship between test performance and aerobic capacity that allows the fitness professional to estimate VO2 max from well-validated prediction equations. Tests can be divided into:
- maximal – to exhaustion
- submaximal – to a percentage of maximum
Accuracy of results will have greater value if the personal trainer records all subjective findings. Subjective data should be recorded at each incremental increase in workload. The following methods can be used:
- RPE – before each exercise test ensure that the client reads and understands the instructions that accompany the RPE scale. RPE is extremely useful to prescribe exercise intensity
- talk test – the talk test has been shown (Norman at el, 2001; ACSM, 2004) to correlate reasonably well with HRR and RPE as a method for estimating exercise intensity
- facial expressions – look for noticeable change in facial expressions/focus
- redness/discomfort – AeT feels comfortable, at the AnT exercise becomes uncomfortable
- breathing rate – as the individual reaches their AeT there will be a steady change from nose breathing to nose and mouth breathing. Sentences can still be completed; however, during sentences one or two pauses for breath are to be expected. As intensity increases breathing rate increases. At ventilatory or AnT breathing rate is rapid. At this point, it will be difficult to hold a conversation/complete sentences
Fitness data tables and tables for interpretation of results have been included in this chapter. Test results will be discussed further in the chapter on designing aerobic fitness programmes.
Alongside screening, pre-testing procedures (Fricker and Fallon, 2000) should be followed in the 24 hours before exercise for accuracy. Finally, to meet health and safety standards PTs should follow the before, during and after exercise test guidelines presented below.
Before the test:
- Exercise is not without risk. The fitness professional has a legal and moral duty to minimise this risk via appropriate screening.
- Inform the client of the exact nature and purpose of the test and obtain his or her written consent to participate
- Ensure all testing equipment and data collection sheets are ready
- Supervise a 3 – 5 minute warm-up (using the same piece of equipment on which the client will be tested)
During the test:
- Control the (predetermined) intensity of the test
- Provide encouragement
- Collect heart rate and RPE data in last 15 seconds of each stage
- Beware of symptoms that demand immediate termination of the test: chest pain; signs of pallor or cold, clammy skin; severe or unusual shortness of breath; wheezing; request of the client; or, confusion or lack of coordination;
- In experienced clients, terminate the test when the client can no longer maintain the required intensity. For beginners, consider terminating the test once the required RPE levels have been reached
After the test:
- Supervise a 3–5 minute cool down.
- Monitor the client for unusual symptoms for a further 10 minutes.
Velocity at V02 max: (vVO2 max):
This concept is based on the work performed by the highly respected French researcher Veronique Billat (1999). She advocates the importance of something called vVO2 max which is the exercise velocity which causes your body to utilise oxygen at its highest possible rate. This has been shown to be a better predictor of ability and performance than VO2 max itself, as it encompasses elements of movement economy and efficiency – or how well the individual moves without wasting effort and oxygen on unnecessary movement. Training at an intensity equivalent to vVO2 max has been shown to not only increase this variable, but also the ability to tolerate the fatiguing effects of lactic acid and movement economy, both of which are key features in enhanced performance. The next question, therefore, is how to calculate vVO2 max and how to use this in programme design. It should be emphasised that this is a test for intermediate to advanced clients who are clear of any risk factors and who are well motivated.
Determining vVO2 max is relatively easy to do. The activity mode chosen obviously depends on the client’s sport and / or chosen activity. The rowing ergometer will be used in this example. After performing an appropriate warm up, the timer on the ergometer should be set to 6 minutes and the display to indicate distance travelled in metres. It is then a simple matter of working as hard as possible for this 6 minute time trial. It is tough and if the client is not used to pacing himself or herself over this duration they may want to have a few attempts to fully optimise performance.
Once the client has completed a good 6 minute effort, the following calculation should be done. Divide the distance travelled by 6 (metres per minute). For example, if the client rowed 1700 metres in 6 minutes this would be 1700/6 = 283.2. This is the vVO2 max in metres per minute. The test should also produce a maximum heart rate for the client as well. Based on the above result exercise intensity can be prescribed. For example: 50% of 283.2 = 141.6 metres per minute.
Balke treadmill test:
Balke and Ware (1959) devised one of the most commonly used treadmill protocols. During the Balke test:
- treadmill speed is set at 3.3 miles per hour (5.3 kilometres per hour) and the initially flat gradient rises to 2%
- increase gradient by 1% with each subsequent minute until the client is unable to maintain the intensity of the exercise
Maximum treadmill time (minutes and fractions of minutes) is directly related to aerobic capacity, and VO2 max can be reliably predicted from the following equation:
VO2 max (ml∙kg-1∙min-1) = 1.444∙(time/60) + 14.99 (Pollock et al., 1976)
For example, a treadmill time of 950 seconds predicts a VO2 max of 37.9 ml∙kg-1∙min-1 [1.444 x (950/60) + 14.99]
- this score can be compared with the VO2 max norms offered in the tables on the next page
Gradual and equal increments make the Balke protocol suitable for many adults, including older and / or deconditioned individuals. However, the test may be too long for more fit individuals. It should be stressed that, due to the gradual nature of the test, no separate warm-up is required.
|Fitness categories for males, based on VO2 max expressed in ml∙kg-1∙min-1|
|AHA, American Heart Association (American Heart Association, 1972)|
|Fitness categories for females, based on VO2 max expressed in ml∙kg-1∙min-1|
|* AHA, American Heart Association (American Heart Association, 1972)|
Cooper 3-mile walk test:
For many individuals, Cooper’s 3-mile walk test provides an indication of aerobic fitness without requiring a maximal effort. As a result, the test is suitable for healthy males and females aged 13–70 years who have been actively walking for at least six weeks (Cooper and Storer, 2001). If the course is accurately measured, the test can be performed indoors or outdoors. Participants should be instructed to walk 3 miles as fast as possible without running. Time to completion can be used to assess aerobic fitness, as indicated in the table on page 153.
Cooper 1.5-mile run test:
Aerobic fitness can be assessed using the 1.5-mile run test first described by Cooper in 1968. The test can provide a valid measure of aerobic capacity, but it requires pacing and a sustained, near-maximal effort. For these reasons, at least six weeks’ aerobic training (preferably running) is recommended before attempting the test. After warming-up, participants should be instructed to complete the 1.5-mile distance as fast as possible. Time is recorded to the nearest second, and a gradual cool-down should follow the test. Interpret test performance using the tables on the following pages. If the Cooper 1.5-mile run test is performed on a treadmill, the incline should be set at 1% to replicate the energy cost of running outdoors (Jones and Doust, 1996).
|Classification of cardiorespiratory fitness based on Cooper 3-mile walk test (Cooper, 1982). Values represent time (min:s) to complete 3-mile walk|
|Age (y)||Very poor||Poor||Fair||Good||Excellent|
|Classification of cardiorespiratory fitness based on Cooper 1.5-mile run test (Cooper, 1982). Values represent time (min:s) elapsed in completing 1.5 miles|
|Age (y)||Very poor||Poor||Fair||Good||Excellent||Superior|
Cooper 12-minute swim test:
Cooper’s swimming test requires the participant to swim as far as possible in 12-minutes using whatever stroke is preferred. Although resting is permitted, an accurate test demands a maximal effort. The easiest way to perform the test is in a pool with known dimensions. It also helps to have another person record the laps and time. Performance can be classified using the table below.
|Classification of cardiorespiratory fitness based on Cooper 12-minute swimming test (Cooper, 1982). Values represent distance (metres) swum in 12- min|
|Age (y)||Very poor||Poor||Fair||Good||Excellent|
Queen’s College step test:
Step tests are useful in assessing cardiorespiratory fitness because they can be administered to individuals or large groups of people without requiring expensive equipment or highly trained personnel. Like most step tests, the Queen’s College step test uses recovery heart rate to assess aerobic fitness (McArdle et al, 1972).
The test is conducted in a single 3-minute period and requires a 41.3 cm (16.25 in) step or platform (which is the same height as many gymnasium bleacher seats). To produce an accurate, repeatable test, a metronome should be set to 88 sounds per minute for females or 96 sounds per minute for males. These rates will ensure that females perform 22 steps per minute whilst males perform 24 steps per minute if the following four-step cycle is followed: on count 1, step up on to the step with one foot; on count 2, step up with the opposite foot, fully extending both legs and the back; on count 3, return the first foot to the floor; and, on count 4, return the second foot to the floor.
At the end of the test, the participant remains standing and heart rate is recorded for 15 seconds beginning precisely 5 seconds after the 3-min stepping period has ended. Convert heart rate to beats per minute by multiplying by 4 and use the following prediction equations to estimate VO2 max (ml∙kg-1∙min-1): males = 111.33 – (0.42 x heart rate); females = 65.81 – (0.1847 x heart rate).
The predicted VO2 max scores can be used to identify fitness categories using the same tables as the Balke treadmill test. Beware, however, that the error associated with this method is 16% of the actual VO2 max.
The multistage fitness test:
Leger and Lambert (1982) first developed a 20-metre shuttle run for the prediction of VO2 max. The ‘bleep test’ is now recognised as one of the most popular and valid tests of aerobic fitness in individuals or groups. The test should be performed on a dry, firm and flat surface with sufficient space for the 20-metre course and sufficient space for deceleration at each end (around 5–10 metres). During the test, participants move between markers whilst the bleep intervals become progressively shorter.
Table of Predicted Maximum Oxygen Uptake Values for the Multistage Fitness Test. Department of Physical Education and Sports Science, Loughborough University, 1987.
|Level||Shuttle||Predicted VO2 max||Level||Shuttle||Predicted VO2 maxuttle||Predicted VO2 max|