The effect of evening swimming exercise on sleep parameters in male swimmers

We evaluated the effects of evening swimming exercise on sleep variables in male swimmers. In a crossover design, 12 competitive male swimmers completed two trials (6:30-8:30 pm): the high-intensity swimming exercise condition (EX) and no-exercise condition (CON). Sleep quality was assessed using electroencephalography, and core body temperature (CBT) was evaluated by the pill type thermometer. Average CBT during the intervention period was significantly higher in EX (37.8°C ± 0.3°C) compared with CON (37.1°C ± 0.2°C, p < 0.05). However, at bedtime (11:00 pm), CBT did not differ significantly between the conditions (37.2°C ± 0.2°C in EX vs. 37.2°C ± 0.3°C in CON, p > 0.05). In EX, the duration and the percentage of rapid eye movement (REM) sleep were significantly lower (81.4 ± 26.7 min in EX vs. 107.6 ± 39.5 min in CON, p < 0.05), and wake after sleep onset was significantly higher (23.5 ± 39.6 min in EX vs. 3.4 ± 2.5 min in CON, p < 0.05). However, other sleep variables did not differ significantly between the conditions (p > 0.05). These findings suggest that evening swimming exercise induced selective rather than generalized impairments in sleep.