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F-13 Thematic Poster - Thermoregulation and Heat Stress Friday, June 3, 2016, 1: 00 PM - 3: 00 PM Room: 110

Does the Rate of Heat Storage Define Exercise Intensity Level During Self-paced Exercise at a Fixed Rating of Perceived Exertion?

2888 Board #2 June 3, 1

00 PM - 3

00 PM

Friesen, Brian J.; Lauzon, Martin A.; Blondin, Denis P.; Haman, Francois; Poirier, Martin P.; Kenny, Glen P.

Author Information
Medicine & Science in Sports & Exercise: May 2016 - Volume 48 - Issue 5S - p 808
doi: 10.1249/01.mss.0000487423.76265.37
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Studies evaluating whether exercise intensity during self-paced exercise at a fixed rating of perceived exertion (RPE) is primarily modulated by the rate of body heat storage have yielded mixed results due to the different methods used to calculate the rate of body heat storage (i.e., thermometry and partitional calorimetry).

PURPOSE: To evaluate via direct calorimetry whether changes in the rate of whole-body heat storage mediates exercise intensity during self-paced exercise at a fixed RPE.

METHODS: Ten trained male cyclists participated in three experimental trials conducted on separate days. Following a 20-min baseline period, participants cycled in a direct air calorimeter during HOT (35°C), NORMAL (25°C) and COOL (15°C) conditions at a fixed RPE of 16, self-regulating their workload in order to maintain this RPE until they could no longer maintain 70% of their starting workload. Whole-body heat loss (evaporative and dry) and metabolic heat production were measured by direct and indirect calorimetry respectively. Body heat storage was measured as the temporal summation of heat production and heat loss.

RESULTS: The starting self-selected workload was lower in HOT compared to NORMAL and COOL (151 ± 30 vs. 165 ± 26 vs. 165 ± 35 W, respectively). Power output declined over time in all conditions (P<0.05), however a faster decrease was observed in HOT (P<0.05). This led to a shorter exercise time in HOT relative to NORMAL and COOL (57 ± 19 vs. 73 ± 22 vs. 68 ± 26 min, respectively). The rate of heat storage decreased over time in all conditions (P<0.05), however it was greater in COOL and lowest in HOT throughout exercise. In general, the rate of heat storage was significantly greater in COOL relative to HOT and greater in NORMAL compared to HOT after the 5th min of exercise. Further, the rate of heat storage was generally greater in COOL relative to NORMAL after the 15th min of exercise (P<0.05). Taken together, the change in body heat storage during exercise was ~2-fold greater during COOL and ~1.5-fold greater during NORMAL compared to HOT (961 ± 438 vs. 740 ± 258 vs. 478 ± 186 kJ, respectively).

CONCLUSIONS: We show that self-paced exercise intensity at a fixed RPE is not primarily mediated by differences in the rate of body heat storage.

SUPPORT: Natural Sciences and Engineering Research Council of Canada (held by Glen P. Kenny).

© 2016 American College of Sports Medicine