Swimming fitness: the truth about testing and monitoring

One thing all endurance athletes need to know is that the endurance training program they are following is effective. If you are trained by a qualified coach of course, you can (hopefully!) place trust in his/her extensive knowledge and experience. However, many amateur and recreational athletes don’t have that luxury, so what do they do? Performing solo time trials is an option but these cannot truly simulate competition. Another option is to race regularly and see how you perform in those races, but what if you’re training for just one or two big events later in the season? That’s not the best time to discover that the training program you’ve been following for months is not particularly effective!

Fitness testing

To overcome these hurdles, a commonly used approach is to undertake fitness testing at regular points through a training program in order to measure key physiological attributes associated with superior endurance performance. Of these attributes, easily the most widely tested is maximum oxygen uptake (or VO2max for short). Why VO2max? The reason is that high levels of VO2max are known to be critical for success in most endurance sports where the event duration exceeds three minutes^(1,2). High levels of VO2max mean that the cardiovascular and respiratory systems are very efficient at delivering oxygen to the muscles involved during exercise, and that those muscles possess an excellent ability to utilize this oxygen for producing the energy required during competitive performance^(3,4).This explains why measuring an athlete’s VO2max is an indispensable tool for researchers, coaches and athletes striving toward excellence in training and performance.

How to test VO2max?

VO2max can be tested in two ways: a) either by testing oxygen consumption at a moderate submaximal intensities and then extrapolating upwards (using predicted maximum heart rate) to estimate maximum oxygen uptake capacity or b) by direct oxygen consumption measurements while performing an incremental test to exhaustion. The former method is less accurate but easy, safe and straightforward to apply in everyday settings. It also forms the basis of a number of simple submaximal fitness monitoring tests (see this article). Direct measurement on the other hand is very accurate but often requires a lab setting with extensive equipment and technicians on hand so is mainly used for elite athlete testing or in research settings.

Regardless of which type of VO2max testing is used, there’s wide agreement about the desirability (where possible) of ‘specificity’ – ie the mode of testing used should most closely reflect the neuromuscular demands of that sport^(5,6). In plain English, this means that to get the most accurate and repeatable results, athletes should undergo exercise testing using the same activity as their own sport – ie runners should be tested while running, cyclists while cycling, rowers while rowing etc.

Testing VO2max in swimmers

Fitness testing specificity is all well and good but it present very significant challenges for the accurate measurement/estimation of VO2max in swimmers swimming in the pool, particularly when accurate measurement is required. This is especially the case given most fitness testing is carried out using treadmills and stationary bikes, which almost exclusively recruit lower body musculature while the athlete is in an upright posture. This is very different to swimming, which relies much more heavily on upper body musculature (in front crawl swimming only about 15 % of the propulsive force is generated by the legs⁽⁷⁾) and takes place in a horizontal posture.

That said, specific modes of fitness testing (ie while actually swimming) for VO2max do exist. One involves free swimming with a metabolic (oxygen uptake) testing system that is carried by someone alongside the pool⁽⁸⁾. But because swimmers have to wear a gas analyzer mask and snorkel, this means they are unable to perform turns since they cannot submerge themselves underwater. Variations in swimming pace can result in a tug on the snorkel, potentially hampering swimming performance and affecting equipment connectivity, thus compromising measurement accuracy. Additionally, it is difficult to increase the exercise load precisely for every step of the incremental test.

Another option is to use a swimming flume (a small pool where the water flow is directed against the swimmer who has to swim at the speed of the flow in order to keep stationary. However, this method is expensive and requires specialized equipment and a dedicated space. Yet another option is tethered swimming, during which the swimmer swims at approximately the same position in the pool with a belt around the waist connected to a pulley system with weights⁽⁹⁾. In tethered swimming, the application of load (and therefore work rate) to the swimmer is easily adjusted; however, a major drawback is that the relative speed between the swimmer’s body segments and the water differs from actual swimming.

Non-specific testing

All of the above testing methods are fairly swimming specific but they involve the complication of using gas analysis mask in an aquatic environment and trained technicians/coaches to help administer the testing. How can amateur swimmers get around these obstacles? The fact is that while swimming specific tests are preferable, incremental fitness testing on land might be more practical for amateurs. One way this can be achieved is by using commercially available swim ergometers, which simulate the swimming action while out of the water, allowing similar arm movements as in water (but without leg involvement)⁽¹⁰⁾.

Another option is to use non-swimming-specific fitness testing measurements such as incremental tests on a stationary bike. While it’s true that such testing involves different muscle activation patterns compared to actual swimming, the measurement of V̇O2max using a stationary bicycle protocol is a standard procedure in many sports because this method is well established, requires almost no technique, and is easy to implement⁽¹¹⁾. More importantly perhaps, studies from a range of endurance sports show that VO2max testing on a stationary bike yields a result that is not too far from that obtained when doing a sports-specific test^(12,13). However, some scientists argue that instead of a stationary bike for VO2max testing, an arm crank (upper body cycle ergometer) might be more appropriate because it relies on upper body muscle recruitment⁽¹⁴⁾, and is more in line with the demands of swimming.

But given the very different muscle recruitment patterns in swimming compared to most sports, how does non-specific VO2max testing compared to swimming-specific testing carried out using a flume or tether? Is it accurate enough to be worthwhile and is there good test–retest reliability? To date, no studies have compared swimming-specific and non-swimming-specific methods of testing VO2max or how the VO2max figure obtained by that testing method relates to real world endurance swimming performance. But now, new research carried out by a team of Dutch scientists has provided some concrete answers.