The effects of recreational underwater exercise in early evening on sleep for physically untrained male subjects

The present study investigated the effects of recreational underwater exercise (UWE; 28.9–31.5°C, 16:00–16:50, 36.2 ± 5.2 %HRres) on thermal response and nocturnal sleep. Rectal temperature (Trec) and sleep parameters of eight physically untrained male subjects were measured in both non‐exercise (NE) and UWE days. Underwater exercise consisted of aerobic exercises with various kinds of movements. During UWE, Trec raised slightly in most subjects, but declined in one subject. We could not observe a rapid decline in Trec before sleep on a UWE day. The polysomnographic and subjective sleep parameters showed no significant differences between NE and UWE nights. The quality of sleep did not improve on the night when UWE was performed, and thermal changes might be related to the results.