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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.

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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.



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.


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.


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.


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.

[Indexed for MEDLINE]

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