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

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

Author information

1
US Army Research Institute of Environmental Medicine, Natick, MA 01760, USA. Robert.Kenefick@us.army.mil

Abstract

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.

PMID:
19461533
DOI:
10.1249/MSS.0b013e3181988c14
[Indexed for MEDLINE]
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