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Med Sci Sports Exerc. 2018 Jan;50(1):159-168. doi: 10.1249/MSS.0000000000001421.

Work Rate during Self-paced Exercise is not Mediated by the Rate of Heat Storage.

Author information

1
1Human and Environmental Physiology Research Unit (HEPRU), School of Human Kinetics, University of Ottawa, Ottawa, ON, CANADA; 2University of Canberra Research Institute for Sport and Exercise (UCRISE), University of Canberra, Bruce, AUSTRALIA; and 3Centre de Recherche du Centre Hospitalier Universitaire de Sherbrooke (CRCHUS) and Faculty of Medicine and Health Sciences, Department of Medicine, University of Sherbrooke, Sherbrooke, QC, CANADA.

Abstract

PURPOSE:

To date, there have been mixed findings on whether greater anticipatory reductions in self-paced exercise intensity in the heat are mediated by early differences in rate of body heat storage. The disparity may be due to an inability to accurately measure minute-to-minute changes in whole-body heat loss. Thus, we evaluated whether early differences in rate of heat storage can mediate exercise intensity during self-paced cycling at a fixed rate of perceived exertion (RPE of 16; hard-to-very-hard work effort) in COOL (15°C), NORMAL (25°C), and HOT (35°C) ambient conditions.

METHODS:

On separate days, nine endurance-trained cyclists exercised in COOL, NORMAL, and HOT conditions at a fixed RPE until work rate (measured after first 5 min of exercise) decreased to 70% of starting values. Whole-body heat loss and metabolic heat production were measured by direct and indirect calorimetry, respectively.

RESULTS:

Total exercise time was shorter in HOT (57 ± 20 min) relative to both NORMAL (72 ± 23 min, P = 0.004) and COOL (70 ± 26 min, P = 0.045). Starting work rate was lower in HOT (153 ± 31 W) compared with NORMAL (166 ± 27 W, P = 0.024) and COOL (170 ± 33 W, P = 0.037). Rate of heat storage was similar between conditions during the first 4 min of exercise (all P > 0.05). Thereafter, rate of heat storage was lower in HOT relative to NORMAL and COOL until 30 min of exercise (last common time-point between conditions; all P < 0.05). Further, rate of heat storage was significantly higher in COOL compared with NORMAL at 15 min (P = 0.026) and 20 min (P = 0.020) of exercise. No differences were measured at end exercise.

CONCLUSIONS:

We show that rate of heat storage does not mediate exercise intensity during self-paced exercise at a fixed RPE in cool to hot ambient conditions.

PMID:
28902126
DOI:
10.1249/MSS.0000000000001421
[Indexed for MEDLINE]

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