Athlete Performance Testing
The Importance of Validity
Whilst there are several different types of test validity, we will consider test validity to be loosely defined as "the ability of a test to measure what it's supposed to". A test with very high validity would have a very high/strong correlation between the the quality it aims to measure (i.e. VO2 Max) and the results of the test (i.e. beep test). Understanding a test's validity is important if we're trying to infer meaning from the results of that test. For example, consider the following:
We have two athletes, athlete's A and B, and we want to find out how has the strongest upper body of the two. One of our tests might be a maximum repetitions chin up test, which we will be completing following a very strict and consistent set of criteria. We find that athlete A did 15 reps, whilst athlete B only managed 10 reps. In this case, it is tempting to consider athlete A to have the stronger upper body of the two, however if athletes are able to complete >10 reps then this test likely doesn't assess maximum strength, and rathe is probably more a test of endurance. It is certainly likely that athlete A is stronger than athlete B, however this test doesn't tell us that directly, rather we have to estimate that based on the results of this test.
Consider the same case, but instead we decided to do a weighted chin-up test, and wanted to find the heaviest weight possible each athlete could do for 3 reps. Assume athlete A was able to do +20kg, whilst athlete B was able to do +15kg, and again the tempting answer would be that athlete A is stronger than B. Whilst this may be a more correct statement than the previous case, what if athlete A weighed 100kg, and athlete B weighed 60kg? Now looking at a relative measure of strength, athlete B is able to lift +25% of their bodyweight, whilst athlete A is only able to lift +20% of their bodyweight. Hence whether this test is valid or not, and/or how you interpret the results will be dependent on what you're hoping this test will tell you! Ranking athletes according to absolute weight lifted might be relevant for a sport like AFL, where the stronger you are the better you are (generally speaking), whereas relative strength might be more important for sports that require peak strength for a given size/weight (i.e. like boxing).
The final thing to consider is the complexity of the test, and how much skill is required to complete it. A highly complicated test may require the athlete "learn" how to do the test, which if not accounted for may result in the athlete scoring poorly in the test. However this poor score is likely due to a lack of familiarisation with the test protocol, rather than a hypothetical reduction in strength, and as such this test may not be a valid measure of strength. Again, consider two athletes (A and B), with different levels of experience with the trap bar deadlift. Athlete A has trained the trap bar deadlift consistently for the last 2 years, whereas athlete B has never deadlifted before in his life. They both complete a 3RM test, with several warm-ups prior to completing the final 3RM effort, and despite athlete B having never deadlifted before in their life, they still manage to lift only 5kg less than athlete A. In this case, there's a strong chance that athlete B is stronger than athlete A, however due to a deadlift requiring some basic technical characteristics and athlete B's naivety of these characteristics they appeared weaker than athlete A.
The above case demonstrates the importance of simple tests to prevent the effect of other variables on the final result and to maximise test validity. However it is worth mentioning briefly that some tests are deliberately complicated in an effort to try mimic sport-specific patterns. For example, consider the basketball lane agility test (video below), which features 7 direction changes, with no 2 direction changes alike. Whilst this test is unlikely to be a highly valid measure of any specific physical quality, its use in basketball suggests that recruiters/selectors consider it to be an important measure of basketball-specific change of direction ability. Hence the test may be a valid measure of basketball specific change of direction ability, but may not be a valid measure of say sagittal acceleration performance (whereas a 10m sprint would be!).
Hence understanding what a test measures is essential to interpreting results from that test, and therefore designing interventions aimed at improving the underpinning physical qualities. For further information regarding specific test validities, we'd encourage you to consult research papers to find out.