Prior heat stress: effect on subsequent 15-min time trial performance in the heat

Med Sci Sports Exerc. 2009 Jun;41(6):1311-6. doi: 10.1249/MSS.0b013e3181988c14.


The impact of prior heat stress on subsequent aerobic exercise-heat performance has not been studied.

Purpose: To determine whether prior heat stress degrades subsequent aerobic exercise performance in the heat.

Methods: Eighteen nonheat acclimated males were trained (four practice trials) on an aerobic exercise performance test in 22 degrees C and then divided into two (n = 8) groups. One group (EUHPH; (.)VO2peak = 44 +/- 7 mL x kg x min(-1)) was tested after 90 min of recovery (in 22 degrees C) from 3 h of intermittent light-intensity (<30% (.)VO2peak) exercise-heat (50 degrees C) stress, where sweat losses were matched with fluid intake (3.5 +/- 0.5 L) to maintain euhydration. The other group (EUH; (.)VO2peak = 45 +/- 5 mL x kg x min(-1)) was tested while euhydrated without prior exercise-heat stress. Aerobic performance was determined from a 30-min cycling preload (50% (.)VO2peak) followed by a 15-min time trial in 40 degrees C. Total work during the 15-min performance time trial in EUH and EUHPH was compared, as were the percent changes from the best practice trials.

Results: Volunteers were euhydrated (plasma osmolality < 290 mOsm x kg(-1)) and normothermic before each exercise-heat trial. Heart rate and core temperature were not different (P > 0.05) between groups at any time point during exercise. Total work was not different (P > 0.05) at baseline or between EUH (150.5 +/- 28.3 kJ; 2.0 +/- 0.3 kJ x kg(-1)) and EUHPH (160.3 +/- 24.0 kJ; 1.8 +/- 0.2 kJ x kg(-1)). The percent change in total work relative to baseline was not different (P > 0.05) between EUH (-18.7% +/- 9.2%) and EUHPH (-15.0% +/- 7.8%).

Conclusions: If hydration and body temperatures recover, prior exercise-heat stress does not result in a greater degradation in aerobic time trial performance in the heat compared with heat exposure alone.

MeSH terms

  • Adaptation, Physiological*
  • Adult
  • Bicycling
  • Body Temperature
  • Body Temperature Regulation
  • Dehydration
  • Ergometry
  • Exercise Test
  • Exercise Tolerance*
  • Exercise*
  • Heat Stress Disorders*
  • Humans
  • Male
  • Muscle Fatigue*
  • Oxygen Consumption*
  • Stress, Physiological*
  • Time Factors