Different effects of heat exposure upon exercise performance in the morning and afternoon

Scand J Med Sci Sports. 2010 Oct:20 Suppl 3:80-9. doi: 10.1111/j.1600-0838.2010.01212.x.


Independent of environmental conditions, rectal temperature follows a circadian rhythm with an acrophase in the late afternoon. In neutral environment, this diurnal increase in temperature is believed to have a passive warm-up effect improving muscle contractility, and in turn, muscle force, power and performance. However, a hot environment blunts the diurnal variation in muscle function by only improving muscle contractility, and in turn, muscle force, power and performance in the morning, when body temperature is at its lowest. Despite this diurnal variation in muscle function, long-duration exercise is only slightly affected by the time-of-day in neutral environment. However, higher afternoon body temperatures can reduce the heat storage capacity and result in a reduction in exercise capacity in hot environments. In addition, in parallel to the circadian variations in muscle contractility and central temperature, exercise capacity in hot environment may also be affected by the diurnal variations in melatonin concentration and in the onset of peripheral vasodilatation and sweating.

Publication types

  • Review

MeSH terms

  • Adaptation, Physiological
  • Body Temperature
  • Body Temperature Regulation / physiology*
  • Circadian Rhythm*
  • Environmental Exposure / adverse effects*
  • Exercise / physiology*
  • Exercise Tolerance / physiology*
  • Female
  • Hot Temperature / adverse effects*
  • Humans
  • Jet Lag Syndrome / etiology
  • Male
  • Melatonin / physiology
  • Menstrual Cycle / physiology
  • Sex Factors
  • Task Performance and Analysis
  • Time
  • Time Factors


  • Melatonin