Testing, testing: time to step on it

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.