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Testing, testing: time to step on it
As the competitive season approaches, monitoring cardiorespiratory fitness becomes increasingly important for endurance athletes. The good news is that keeping tabs on your progress can be achieved simply, quickly, and with virtually no technology. SPB explains
If you want to know where you’re heading, you need to know where you’re starting from. You might think that this is a self-evident statement, but you’d be amazed just how many (especially recreational) endurance athletes blunder from workout to workout without even the vaguest idea of how effective their training actually is.
While progress in strength training is easy enough to monitor (you know how many reps you can lift for each exercise, and at what weight), assessing less tangible parameters such as aerobic capacity and lactate threshold is more difficult. The ultimate way of monitoring endurance performance of course is to race against the clock over a set distance. However, many recreational athletes do not compete regularly, and instead focus on one or two big events each year. In these circumstances, it’s harder to be confident that the training program you are following is delivering the goods.
Flat-out time trials are another way of testing progress but they are potentially draining, requiring very high levels of motivation for a lone athlete, and may also interfere with day-to-day training thanks to the much longer recovery period required. The good news is that it’s possible to get a reasonably reliable handle on your endurance progress (or lack of it) by performing a lower-intensity ‘sub-maximal’ aerobic test.
The pros and cons of sub-maximal testing
One of the most fundamental parameters for determining endurance capacity is maximum aerobic power, which is commonly abbreviated as VO2max(1). VO2max describes the maximum capacity of the body to absorb, transport and deliver oxygen to exercising muscles, and is measured in millilitres of oxygen per kilo of bodyweight per minute (mls/kg/min). This is a crucial parameter because unlike carbohydrate and fat (the other components of fueling energy production), oxygen cannot be stored in the body. Therefore, the faster oxygen can be absorbed and delivered to working muscles, the higher the intensity of exercise that can be sustained.
More sophisticated measures of endurance performance
Over the last twenty years or so, it’s true that more sophisticated measures of endurance performance have emerged for assessing endurance capacity in a race situation – for example, maximal lactate steady state’ (MLSS - defined as the maximum workload that the body can sustain without the rapid accumulation of lactate in the bloodstream)(2,3). But the problem with using a measure such as MLSS is that it requires lactate monitoring technology and a lab environment for testing, which is beyond the means of nearly all independent and recreational athletes. This is why simple sub-maximal testing usually targets estimates of VO2max, which can be carried out in a home or gym environment.
A sub-maximal test for aerobic power essential measures oxygen carrying ability at ‘part-throttle’ and then uses theoretical maximum heart rate to extrapolate upwards and predict the maximum oxygen carrying power if you were forced to work flat out. Although considerably less accurate than a maximal test, there are certain advantages, including the following:
• For starters, athletes who test this way will not have to suffer the “I’m going to die/vomit/faint” feeling that inevitably follows, as anyone who’s done a maximal test will confirm!
• Secondly, the reasonably gentle nature of the test means that it can easily be slotted in before a workout and then training continued as normal.
• Thirdly, sub-maximal tests are much more suitable for novice and older athletes; maximal testing carries a small but significant risk of a cardiac event in those without a solid endurance training background – a risk that is accentuated as the years tick by(4). [NB – this should be borne in mind by coaches of novice or older athletes, and also explains why most fitness clubs and sports centres that offer fitness assessment procedures invariably use sub-maximal testing.]
Carrying out testing
Sub-maximal aerobic power tests only require two actual measurements to be made at most. The first is what the energy output is. This is because to produce energy the body needs to ‘burn’ fuel in the presence of oxygen. Since it takes roughly a litre of pure oxygen to produce 5kcals of chemical energy, if you know someone’s power output in calories per minute (or in the other frequently used units i.e. Watts) then you know how much oxygen they’re using. Thus someone who is burning 600 calories per hour is using 10 calories per minute or two litres of oxygen per minute.
The second thing you have to know is the heart rate. It just so happens that over much of the heart rate range, there is a fairly linear relationship between the heart rate and the amount of oxygen being consumed. This means that if you know how much oxygen is being consumed at a ‘sub-maximal’ (and comfortable) heart rate and you know the theoretical maximum heart rate, then you can extrapolate upwards to calculate someone’s theoretical VO2 max – ie maximum oxygen consumption in litres per minute if pushed flat out (at which point their heart rate would hit its maximum).
Finally, because bigger bodies need bigger engines to drive them, dividing the maximum oxygen uptake figure (in litres per minute), by weight in kilos will tell you how much oxygen (and therefore energy) each kilo of body weight has to play with at full-throttle. This gives a good indication of performance capabilities in most endurance sports where athletes have to contend with gravity (ie where weight affects performance – eg running, road and mountain biking and triathlon). Where there’s no impact of gravity and body weight is supported (eg rowing, track cycling), absolute V02max may be a more useful measure of performance.
A box is fine
Many sub-maximal aerobic power tests use a stationary bike to provide the constant energy demand. While this is fine provided the bike has been properly calibrated to deliver the workload it should (you’d be surprised how many don’t!) there’s an even easier way by using the ‘Queens College Step Test’. This simple step test requires nothing more than a step, bench or box with a height of 16.25 inches (41.3cms), a metronome and a watch with a second hand. Originally devised by one of the true pioneers of exercise physiology, Professor William McArdle, the Queens College Step Test provides a simple, quick and reasonably reliable estimation of maximal aerobic capacity(5,6).
It’s a little different from the commonly used sub-maximal tests in that it uses recovery heart rates rather than mid-exercise heart rates and doesn’t utilise predicted maximum heart rates. This is a good thing since predicted maximum heart rate figures can be unreliable (especially in athletes with a long training background) and introduce significant error. More importantly, this step test has excellent retest reliability, which means that it is a very useful tool for tracking aerobic fitness changes over time in the same person – handy if you want to keep tabs on your progress. More generally, there’s also a very solid evidence base for the use recovery heart rates for the estimation of aerobic capacity. Cross sectional studies show that physically active individuals have improved heart rate recoveries compared to their sedentary counterparts(7-10).
In addition, research shows that both VO2max and heart rate recoveries improve following an exercise regimen in longitudinal studies(11-13). This means that using heart rate recovery is an effective means of monitoring the training adaptations produced by an endurance program. Finally, research also shows that heart rate recoveries and VO2max are highly associated in studies that include older adults, athletes, and physically active individuals(14-17). This doesn’t necessarily mean that measuring heart rate recovery will provide a highly accurate estimate of VO2max. But what is does mean that as VO2max improves, those gains can be accurately tracked using improvements in heart rate recovery.
How to do it
The test itself is very quick and simple. The subject steps up and down on a 16 and ¼ inch high box or bench for three minutes in a ‘right leg up left leg up, right leg down left leg down’ fashion. The rate of stepping is 22 steps per minute for females and at 24 steps per minute for males. This constant rate is ensured by the use a metronome (there are many free metronome apps available for smartphones). On completion of the test, the subject immediately stops and sits on the platform for 5 seconds after which the heartbeats are counted for 15 seconds (i.e. heartbeats counted from seconds 5-20 after the stepping). The number of heartbeats counted is then multiplied x 4 to give heart rate in beats per minute. To calculate approximate VO2max in millilitres of oxygen per kilo of body weight per minute, this heart rate in beats per minute is then plugged into one of the two following formulae:
• Men – VO2 max = 111.33 – (0.42 X heart rate)
• Women – VO2 max = 65.81 – (0.1847 X heart rate)
There’s no need to take weight into account when using this test as it is effectively factored out by the test – stepping up and down on a bench against the force of gravity means that those with higher body weights work at higher energy outputs
For those of you who don’t wish to use the above formula, an easy to read table is supplied below – just read off your estimated VO2max figure from your post-test heart rate. Remember though, this is an approximation of your VO2max – not an actual measurement. What’s important however is that as your VO2max (hopefully) improves, your score on this test will also improve. Therefore, you can regard this as a simple and reliable method of tracking your endurance fitness over a period of weeks and months. Remember too that while this test has high inter-test reliability for an individual, it is not appropriate to compare your score with that of someone else’s. This test is only designed to compare your performance now with your performance at a later date - ie track your changes over time.
Other uses
A final point is that using a reliable and repeatable sub-maximal test, which incorporates heart rate measurement is useful in other ways. Once a baseline has been established, a test such as this can pick up changes unrelated to fitness. For example, a mild viral infection is known to raise heart rate for a given effort level(18). If you feel out of sorts therefore, and this step test shows a sudden deterioration in performance (ie higher than expected heart rate), there’s a good chance you’re fighting off an infection – in which case, take it easy for a few days! The same elevation in heart rate for a given workload effect is true where athletes become fatigued, or even overtrained(19). Once again, this means that an unexpectedly poor result might indicate you have been overdoing things with insufficient recovery.
Table: Predicted/estimated VO2max based on recovery heart rates
|
FEMALE |
MALE |
||
|
Recovery Heart Rate (bpm) |
Predicted VO2 Max (mls/kg/min) |
Recovery Heart Rate (bpm) |
Predicted VO2 Max (mls/kg/min) |
|
90 |
49.2 |
90 |
73.5 |
|
95 |
48.3 |
95 |
71.4 |
|
100 |
47.3 |
100 |
69.3 |
|
105 |
46.4 |
105 |
67.2 |
|
110 |
45.5 |
110 |
65.1 |
|
115 |
44.6 |
115 |
63.0 |
|
120 |
43.6 |
120 |
60.9 |
|
125 |
42.7 |
125 |
58.8 |
|
130 |
41.8 |
130 |
56.7 |
|
135 |
40.8 |
135 |
54.6 |
|
140 |
39.9 |
140 |
52.5 |
|
145 |
39.0 |
145 |
50.4 |
|
150 |
38.1 |
150 |
48.3 |
|
155 |
37.2 |
155 |
46.2 |
|
160 |
36.3 |
160 |
44.1 |
|
165 |
35.3 |
165 |
42.0 |
|
170 |
34.4 |
170 |
39.9 |
|
175 |
33.3 |
175 |
37.8 |
|
180 |
32.6 |
180 |
35.7 |
|
190 |
30.7 |
190 |
33.3 |
References
1. Heyward V.H. Advanced Fitness Assessment and Exercise Prescription. 6th ed. Human Kinetics; Champaign, IL, USA: 2010. pp. 65–101
2. Med Sci Sports Exerc. 2001;33(12):2089–2097
3. Med Sci Sports Exerc. 2005;37(10):1734–1740
4. Arch Cardiovasc Dis. 2017 Mar;110(3):149-156
5. Med Sci Sports. 1972 Winter;4(4):182-6
6. McArdle, Katch and Katch "Exercise Physiology: "Nutrition, Energy, and Human Performance". 8th edition, March 2014. Lippincott Williams and Wilkins
7. Am J Physiol 1988;254(2 Pt 2):H340–3
8. Cardiovasc Res 1992;26(7):713–9
9. J Sports Sci Med 2005;4(1):9–17
10. J Sports Sci Med 2011;10(2):369–75
11. Eur J Appl Physiol 2001;85(3–4):259–63
12. J Am Geriatr Soc 2005;53(11):2037–8
13. Eur J Appl Physiol 2019;119(9):2095–103
14. J Heart Lung Transplant 2006;25(8):942–5
15. J Strength Cond Res 2017;31(4):1055–61
16. Res Sports Med 2021:1–14. Sci Rep 2021;11(1):3620
17. BMC Public Health. 2020;20:1012
18. Mil Med. 1985 Jan;150(1):8-14
19. Int J Sports Med. 1991 Oct;12(5):444-52
Andrew Hamilton
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