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Swimming fitness: the truth about testing and monitoring
SPB looks at new research on how best to assess VO2max in swimmers - a key determinant of swimming performance – and the surprising conclusions reached
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.
New research
In this study, which was published last month in the Journal of Science and Medicine in Sport, the scientists investigated the accuracy and repeatability (how consistent repeated measurements were) of four different methods of VO2max testing for swimmers(15). Fourteen male and six female competitive swimmers (average age 18.7 years) were recruited for the study and on four separate occasions in a randomized order, performed four maximal incremental exercise tests to assess VO2max. These tests used the following modes of exercise:
· Stationary cycling
· Arm cranking
· Ergometer swimming or dry land
· Tethered stationary swimming in a pool
In each of the four assessment methods, the swimmers started at a low load/speed, with the load/speed increased every two minutes until the participant could no longer continue. During this process, continuous breath-by-breath gas analysis was used to determine oxygen consumption, with the VO2max being recorded at the point of exhaustion just before exercise was terminated. In addition, heart rates were monitored at all times during testing. One to two weeks after these VO2max assessments had been completed, all the swimmers performed a 1500m time-trial swim to see how closely each VO2max score from the four assessment methods correlated with their actual performance. In addition, nine male swimmers and two females repeated the tethered swimming test twice to examine the test–retest reliability.
What they found
Since tethered swimming was the most specific mode of testing (and therefore potentially the most accurate and relevant method of assessing VO2max), the researchers expected that the other reasonably specific modes of testing - the ergometer swimming test, and to a lesser extent, the arm cranking test - would prove superior to the bicycle testing. But that is not at all what emerged from the data. It turned out that the tethered swimming and the bicycle test yielded almost identical measures of VO2max (54.40 and 54.39mls/kg/min respectively) – see figures 1 and 2. By contrast, the supposedly more swimming-specific tests using the arm crank and swim ergometer tests yielded significantly lower (and inaccurate) estimates of VO2max (43.14 and 40.54mls/kg/min respectively).
Figures 1&2: VO2max results using different test modes & tethered swimming comparisons
Figure 1 (top): Each dot, triangle or diamond represents an individual swimmer. The middle horizontal line represents the average score in that test. Tethered swimming (purple dots) and stationary biking (turquoise triangles) produced near identical results indicating a high level of accuracy. Arm cranking and the swim ergometer both yielded results that were way off tethered swimming and biking (shown by the black statistical difference bars at the top).
Figure 2 (bottom): The grey line represents the reference scores from the tethered swimming test. The closer scores are from other methods to that line and more tightly clustered around that line, the more accurate and relevant is that method. As you can see, VO2max testing using the bike produced tightly clustered scores almost on the grey line, whereas the arm cranking and ergometer results were more poorly related to the tethered swim test results.
The real kicker however came in the 1500m time trial test to see how relevant and closely correlated the VO2max score from each method was to swim times. Here, the bicycle VO2max score was most closely correlated to 1500m time trial, with a correlation score of 0.655 (scores range from 1.0 = perfect correlation to 0.0 = zero correlation) – see figure 3. This means the bike VO2max score was able to account for over 65% of the variance in swim times. Tethered swim results had a correlation score of 0.641, while the ergometer swim result scored 0.638. The arm crank test meanwhile scored just 0.413. Overall, the researchers concluded that bike, tethered swimming and swim ergometer testing are useful for tracking likely performance in a 1500m swim test but that arm cranking should not be used.
Figure 3: Relation between the VO2max estimates 1500m time trial times
Practical implications for swimmers and coaches
As highlighted by the study authors, key five take-home recommendations emerge from this study:
· An arm crank test is not recommended for determining VO2max in swimming. Arm cranking shows notably lower validity (24 % worse) than the other methods, making it inferior for evaluating the endurance capacity of swimmers.
· A swim ergometer test underestimates the actual VO2max during swimming but nevertheless shows a strong capacity to predict 1500-m time trial performance – nearly on a par with the bicycle and tethered swimming tests. It can therefore be recommended as a testing mode for swimmers.
· Bicycle and tethered swimming tests are the best methods for determining VO2max in swimming and are most closely correlated to actual swim performance in a 1500m test. In terms of validity they can be used interchangeably, which means that swimmers and coaches can use a bicycle test to generate valuable information about progress in endurance swimming.
· The authors recommend that when the equipment and expertise is available, a tethered swimming test might be more suitable for measuring maximal oxygen consumption and other physiological variables, such as heart rate, which can then be used in practice for load monitoring and establishing training zones.
· When aiming to monitor VO2max over a period of time, a bicycle test is superior, especially because it only needs a single supervisor who provides instructions, monitors cadence, supervises the test, and encourages the participant. Furthermore, the bicycle ergometer test can be conducted in any well-ventilated room.
One final point is that all of these tests used direct measurements of VO2max (ie directly measuring oxygen consumption using gas analysis). Indirect measurement, where testing takes place at a submaximal work rate with VO2max predicted from a heart rate extrapolation, was not used. However, there’s no particular reason to believe that bike testing of VO2max using indirect measurement would not be equally appropriate for assessing swimmers aerobic fitness levels. If you’re an amateur swimmer without access to a coach or direct measurement facilities, but you are able to get hold of an accurately calibrated stationary bike, the video below by ’Physiotutors’ provides an excellent step-by-step guide on assessing your own VO2max using a submaximal cycling test.
References
1. J Physiol. 2008; 586: 35-44
2. Front Sports Act Living. 2021; 3719434
3. J Appl Physiol. 2016; 121: 636-645
4. Med Sci Sports Exerc. 2000; 32: 70-84
5. Br J Sports Med. 1995 Sep;29(3):153-7
6. J Sports Med Phys Fitness. 2012 Jun;52(3):245-54
7. Biomechanics in Sport: Performance Enhancement and Injury Prevention. 9. 2000: 205-231
8. J Appl Physiol. 1971; 30: 733-738
9. J Appl Physiol. 1980; 48: 232-235
10. Sports. 2019; 7: 234
11. Int J Environ Res Public Health. 2023; 20: 2995
12. J Appl Physiol. 1961; 16: 977-981
13. J Appl Physiol. 1976; 41: 191-196
14. J Strength Cond Res. 2010; 24: 2809-2815
15. J Sci Med Sport. 2024 Apr 4:S1440-2440(24)00112-9. doi: 10.1016/j.jsams.2024.03.015. Online ahead of print
Andrew Hamilton
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