I've also found the same with the beep test. If you have a high level of fitness, it is the speed at which you can swim the 25m that is the limiting factor, not fitness.

I think the 200m test that Hamish did may be the one that David Lambert made us do which was more of an endurance test. From memory it was 5 x 200m surface swimming with fins with a 1-2 minute break in between each one. Time was recorded for each 200m and the fitter you were the more constant the times were (ie you were able to maintain your times without dropping off towards the end). Again, swimming speed is a limiting factor but as long as you only look at your own times and improvements in them, and not compare them to others, it can be a useful test.

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