Investigating The Impact Of Circuit Training In The Heat On Sleep And Recovery

Acute exertional heat exposure can disrupt sleep and recovery, though adaptation may occur with multiple heat exposures to mitigate this negative effect. PURPOSE: This study investigates the effects of circuit training in the heat on post-exercise sleep and recovery. METHODS: Seven trained men (Mean±SD; age: 23±3 yrs, height: 175.9±11.5 cm, weight: 82.0±16.4 kg) completed 5 days of circuit training in the heat (35°C, 40% relative humidity), which consisted of 40 min of sprinting, and upper and lower body functional exercises. Objective sleep and recovery were monitored with a wearable fitness monitoring device on each night during the study period. Additionally, subjective sleep and fatigue were tracked with a modified Karolinska Sleep Diary, which was completed prior to each session for the previous night. A repeated measures ANOVA with A Bonferroni post hoc test was used to analyze the data. RESULTS: Objective measurement of the time to fall asleep was longer the night after day 4 (25.4±4.0 min) compared to baseline (15.3±4.7 min, p=0.022), which is a 3-day average prior to the start of training. However, the time to fall asleep on day 5 was shorter compared to day 4 (11.1±6.8 min, p=0.004). Subjective fatigue increased on the night after day 2 (3.7±0.9) compared to baseline (1.9±0.6, p=0.019). No significant changes on other objective measures (heart rate variability, recovery index score, sleep efficiency, duration of total sleep, rapid eye movement, light or deep sleep) or subjective measures (ease of falling asleep or waking up, soreness) on sleep and recovery were seen over time (p>0.05). CONCLUSION: These findings suggest that circuit training in hot conditions may temporarily impair the time to fall asleep and increase perceived fatigue, though adaptive responses may occur with continued exposure. Overall, short-term circuit training in the heat appears to have minimal lasting effects on objective and subjective sleep and recovery measures in trained men.