Evidence that heat acclimation training may alter sleep and incidental activity

John O. Osborne, Geoffrey M. Minett, Ian B. Stewart, Stewart Trost, Christopher Drovandi, Joseph T. Costello, Toby G. Pavey, David N. Borg

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This randomized cross-over study tested the hypothesis that heat acclimation training would detrimentally affect sleep variables and alter incidental physical activity compared to a thermoneutral training control condition. Eight recreationally trained males (VO2peak 49±4.9 mL.kg-1.min-1) completed two separate interventions separated by at least 31 days: 5 consecutive day training blocks of moderate-intensity cycling (60 min·day-1 at 50% peak power output) in a hot (34.9±0.7 °C and 53±4 % relative humidity) and a temperate (22.2±2.6 °C; 65±8 % relative humidity) environment. Wrist-mounted accelerometers were worn continuously for the length of the training blocks and recorded physical activity, sleep quality and quantity. Data were analysed in a Bayesian framework, with the results presented as the posterior probability that a coefficient was greater or less than zero. Compared to the temperate training environment, heat acclimation impaired sleep efficiency (Pr β<0 = .979) and wake on sleep onset (Pr β>0 = .917). Daily sedentary time was, on average, 35 min longer (Pr β>0 = .973) and light physical activity time 18 min shorter (Pr β>0 = .960) during the heat acclimation period. No differences were observed between conditions in sleep duration, subjective sleep quality, or moderate or vigorous physical activity. These findings may suggest that athletes and coaches need to be cognisant that heat acclimation training may alter sleep quality and increase sedentary behaviour.
Original languageEnglish
Pages (from-to)1731-1740
JournalEuropean Journal of Sport Science
Issue number8
Early online date15 Sept 2022
Publication statusPublished - 1 Aug 2023


  • Extreme environments
  • actigraphy
  • physical activity
  • training load
  • perceived exertion
  • stress


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