The authors have declared that no competing interests exist.
Swimming is a human activity that relies heavily on individual physiological capabilities. In fact, the swimming general performance equation, proposed several years ago by di Prampero
These (and other) limitations leaded to the emergence of a number of functional tests, used frequently in swimming daily practices, some of them based on continuous exertions, as the 30 min, 2000 m and maximal lactate steady state tests
Critical velocity is expressed as the slope of a straight line established between, at least, two swimming distances and their corresponding exercise durations, i.e., the slope of the regression line determined between the test distances and the time needed to cover them at maximum intensity. This is an easy to accomplish test that allows evaluating the maximal velocity of a swimmer in a regime of physiological aerobic balance
So, critical velocity might be an excellent alternative to non-invasive measurements in swimmers physiological evaluation and respective training control but coaches and exercise physiologists should be careful with its determination, particularly by always including a test distance that depends greatly on energy of aerobic provenience (of, at least, 15 min). In fact, if they do not choose the most adequate testing distances/durations, significant errors might happen when analysing training and predicting performance, limiting significantly the application of information to the training process. If critical velocity is assessed respecting its methodological meaning, it could be very useful for the determination of training intensities, particularly on the moderate intensity domain (also known as aerobic capacity). Swimming below that pace will be optimal for warming up and recovering routines (low intensity domain) and swimming slightly higher the critical velocity will recruit the anaerobic metabolism in a significant way (heavy intensity domain), even though not reaching maximal oxygen uptake.