Are All Heat Loads Created Equal?

作者：Meade Robert D; Kenny Glen P^*

来源：Medicine and Science in Sports and Exercise, 2017, 49(9): 1796-1804.

DOI：10.1249/MSS.0000000000001309

• SWEATING
• CORE TEMPERATURE
• HEAT BALANCE
• THERMOREGULATION
• HEAT STRAIN
• EXERCISE

Purpose: We evaluated physiological responses during exercise at a fixed evaporative requirement for heat balance (E-req) but varying combinations of metabolic and environmental heat load. Methods: Nine healthy, physically active males (age: 46 +/- 8 yr) performed four experimental sessions consisting of 75 min of semirecumbent cycling at various ambient temperatures. Whole-body dry heat loss (direct calorimetry) was monitored continuously as was heat production (indirect calorimetry), which was adjusted to achieve an E-req of 400 W. The resultant metabolic heat productions and ambient temperatures for the sessions were as follows: (i) 440 W and 30 degrees C (440 [30]), (ii) 388Wand 35 degrees C (388 [35]), (iii) 317Wand 40 degrees C (317 [40]), and (iv) 258Wand 45 degrees C (258 [45]). Whole-body evaporative heat loss was determined via direct calorimetry. Esophageal (T-es) and mean skin (T-sk) temperatures as well as HR were monitored continuously. Mean body temperature (Tb) was calculated from T-es and T-sk. Physiological strain index (PSI) was determined from T-es and HR. Results: Endexercise evaporative heat loss and Tb were similar between conditions (both P >= 0.48). T-es was greater in 440 [30] (37.67 degrees C +/- 0.04 degrees C) and 388 [35] (37.58 degrees C +/- 0.07 degrees C) relative to both 317 [40] (37.35 degrees C +/- 0.06 degrees C) and 258 [45] (37.20 degrees C +/- 0.07 degrees C; all P <= 0.05). Further, T-sk was different between each condition (440 [30], 33.85 degrees C +/- 0.16 degrees C; 388 [35], 34.53 degrees C +/- 0.08 degrees C; 317 [40], 35.67 degrees C +/- 0.07 degrees C; and 258 [45], 36.54 degrees C +/- 0.08 degrees C; all P < 0.01). In 440 [30], HR was elevated by about 13 and 18 bpm relative to 317 [40] and 258 [45], respectively (both P < 0.01). Finally, PSI was greater in both 440 [30] and 388 [35] compared with 317 [40] and 258 [45] (all P <= 0.04). Conclusions: Exercise at a fixed E-req resulted in similar evaporative heat loss and T-b. However, the T-es, T-sk, HR, and PSI responses varied depending on the relative contribution of metabolic and environmental heat load.

• 出版日期2017-9