The aim of this study is to validate a swimming test to measure Maximal Aerobic Speed (MAS) as a training rhythm prescription. 7 triathletes and swimmers swam 400 m at maximal speed, then they made a progressive test in order to measure MAS. One week later, maximum time and distance at MAS were measured, and the individual anaerobic threshold (IAT) was determined by a progressive swimming test composed of six repetitions of 200 m at different speeds. One week later, the two first tests were repeated (retest). Taking into consideration that the sample was composed by very few athletes, and that test repeatability was a little higher than expected, the time that swimmers were able to maintain MAS was close to the value that some authors assign to the capacity of maintaining VO2max. The VO22max was higher in the MAS test than in the 400m crawl, although at slower speeds. This would mean that swimmers achieve intensities near VO22max at the MAS test, although not at 400m maximal speed test.<\/p>\n\n