Impact of sleep deprivation on heat-related illness in females when exercising

This project was the first research to investigate acute sleep deprivation in females.

Physically stressful occupational and athletic activities performed in hot ambient conditions are associated with an increased physiological strain and impaired endurance performance. It has been proposed that those who suffer sleep deprivation (full or partial) are less tolerant in hot environments due to reduced sweat rate, increased ratings of exertion and increased core temperature. As a consequence, sleep deprivation has been discussed as a predisposing factor for heat-related illness.

There is limited and inconclusive evidence surrounding the physiological and perceptual responses while sleep deprived, especially for females when acknowledging differences in thermoregulatory function between sexes. This research project investigated the impact of acute 24-hour sleep deprivation on the perception of heat-related illness without physiological consequences in females exercising at a fixed metabolic heat production.

The aim of this study was to quantify the effect of acute sleep deprivation (24 hours) on perceptual markers related to heat-related illness (HRI) and physiological strain in females.

It was hypothesised that sleep deprivation would increase the perception of symptoms of HRI, determined by an increased heat illness symptom index (HISI) score. Secondly, that sleep deprivation would significantly increase rate of core temperature rise due to reductions in heat dissipation.

Nine recreationally active females completed three trials in hot conditions (40°C, 40 per cent relative humidity), during the follicular phase of the menstrual cycle. Participants completed a threshold-maximal preliminary trial, followed by two 30-minute runs at speeds equating to a metabolic heat production of 10W.kg-1, with the last trial following sleep deprivation for 24 hours.

The perceptual indicators of heat-related illness were higher when sleep-deprived; with a HISI score of 28 ± 16 compared to 20 ± 16 in the non-sleep deprived trial, P < 0.05 (Figure 1), in line with the primary hypothesis. Contrary to the secondary hypothesis, rate of core temperature rise did not differ between trials.

There were no differences in physiological responses between the two trials for any of the variables, as seen in Table 1 (core temperature, mean skin temperature, heart rate, sweat rate, thermal sensation or ratings of perceived exertion). The only significance observed was average heart rate was lower when sleep-deprived (180 ± 7 vs. 182 ± 7 beats.min-1).

This was the first research to investigate acute sleep deprivation in females, while controlling for individual alterations to a stressor accurately, by accounting for metabolic heat production during a heat stress test under uncompensable heat stress.

The novel findings are that 24-hour sleep deprivation increased the perception of symptoms related to heat related illness, but had no effect on thermoregulatory function. These findings emphasise that contrary to previous literature, female athletes, occupational workers or military personnel who experience an acute bout of sleep deprivation (24 hours) during shift work or travelling to a hot climate, will not incur an enhanced physiological strain during high intensity exercise

Publications
Relf, R. (2016) Acute sleep deprivation increases perceptual indicators of heat-related illness without physiological consequences in females. British Association of Sport and Exercise Sciences Annual Student Conference, Bangor, 22-23 March.

Rebecca Relf was winner of the Postgraduate Applied Research Award at the BASES 2016 Student Conference in Bangor.