Effects of intensified endurance training on nocturnal skin temperature and sleep variables in male long-distance runners: A pilot study.

This study examined the effects of intensified endurance training on nocturnal skin temperature and sleep variables in male long-distance runners. Fourteen runners completed two different 8-day training programs: one with intensified training (INT) and one with normal training (NOR). At night, proximal (chest) skin temperature was measured every 5 min. Sleep variables, including efficiency, total time, latency, and wake time after sleep onset (WASO), were assessed for 8 consecutive days. Running distance over 8 days was significantly higher in INT (209.2 ± 17.4 km) than in NOR (118.5 ± 31.2 km, p = 0.01). Maximum skin temperature was significantly higher (p = 0.045) throughout the night in INT, especially during the first 180 min after bedtime (p = 0.03). Delta (Δ) skin temperature (maximum - minimum) during sleep was higher in INT than in NOR (p = 0.004). Sleep latency was significantly longer in INT (8.4 ± 4.0 min) than in NOR (2.6 ± 1.9 min, p = 0.003). Eight consecutive days of intensified endurance training elevated nocturnal proximal skin temperature with increased sleep latency. These findings suggest that increased training volume may alter nocturnal thermoregulatory responses and delay sleep initiation without substantially impairing overall sleep quantity.