Cardiac size and VO2max do not decrease after short-term exercise cessation.

We measured maximum oxygen uptake, estimated changes in plasma volume, and the cardiac dimensions of 15 male competitive distance runners (28.2 +/- 5.6 yr of age, mean +/- SD) before and after 10 days of exercise cessation. Subjects were habitually active but adjusted their training to run 16 km daily for 2 wk before the study. Subjects were maintained on defined diets for the week before and during the detraining period. Average body weight decreased 1.0 +/- 0.5 kg (P less than 0.001) within 2 days of exercise cessation and was accompanied by a 5.0 +/- 5.9% (P less than 0.01) decrease in estimated plasma volume. No additional changes in body weight and plasma volume occurred during the study, and estimated percent body fat did not change. Resting heart rate, blood pressure, and cardiac dimensions were also unchanged with physical inactivity. In addition, maximum oxygen uptake was not altered although peak exercise heart rate was an average of 9 +/- 5 beats X min-1 (P less than 0.01) or 5% higher after detraining. We conclude that short periods of exercise cessation decrease estimated plasma volume and increase the maximum exercise heart rate of endurance athletes but do not alter their cardiac dimensions or maximum oxygen uptake.