Investigating the effects of high temperature bathing on deep sleep immediately after sleep onset

Abstract

【Background】

High-temperature bathing has not been considered effective due to a lack of evidence in healthcare. Based on previous studies showing that high skeletal muscle mass is associated with poor sleep during the summer months, we targeted individuals who train on a daily basis. To observe the effect of increased deep body temperature, including the heating effect of high temperature and the pressure effect of immersion, on sleep, with a particular focus on falling asleep, and the effect of increased percentage of deep sleep within 1.5 hours of sleep onset.

【Methods】

Subjects were 12 citizens in their 30s and 40s, muscular individuals (10 men and 2 women) who train daily. Bathing was with a total of at least 10 minutes of immersion of 3-5 minutes each, at 40°C for appropriate bathing and 42°C or higher for high temperature bathing, regardless of interval or total time. Measurements were made by continuous heart rate measurement using a wearable device, and the effects on deep sleep due to the heart rate attained during bathing and the sympathetic and parasympathetic nervous system balance were determined.

【Results】

Sleep efficiency was good for the summer season, but did not improve with high-temperature bathing. As an effect of bathing in hot springs, there was a slight but non-significant increase in deep sleep duration. Both mean and median deep sleep latency were also shortened, but not significantly.

【Conclusion】

As an effect of bathing in high-temperature hot springs during the summer, the deep sleep latency also tended to shorten, although this was not significant. However, although the bathing conditions were considered to be too severe in summer, the increase in heart rate during bathing suggested that it was not a burden for the subjects. The need to select subjects for the effects of high-temperature bathing was felt, taking into consideration that a large part of the effects of high-temperature bathing depended on the state of sleepiness in daily life. It was also considered necessary to set bathing conditions for high-temperature bathing based on the heart rate reached by the individual.