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A retrospective analysis to determine if exercise training‐induced thermoregulatory adaptations are mediated by increased fitness or heat acclimation
Author(s) -
Ravanelli Nicholas,
Gag Daniel,
Imbeault Pascal,
Jay Ollie
Publication year - 2020
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/ep088385
Subject(s) - vo2 max , thermoregulation , acclimatization , aerobic exercise , zoology , heat stress , running economy , heart rate , chemistry , medicine , biology , ecology , blood pressure
New FindingsWhat is the central question of this study? Are fitness‐related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacityV ̇O 2 maxor is it the partial heat acclimation associated with training?What is the main finding and its importance? During uncompensable heat stress, individuals with high and lowV ̇O 2 maxdisplayed similar sweating and core temperature responses whereas exercise training in previously untrained individuals resulted in a greater sweat rate and a smaller rise in core temperature. These observations suggest that it is training, notV ̇O 2 maxper se , that mediates thermoregulatory improvements during uncompensable heat stress.Abstract It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumptionV ̇O 2 max , independently improves heat dissipation in uncompensable environments, or whether the thermoregulatory adaptations associated with heat acclimation are due to repeated bouts of exercise‐induced heat stress during regular aerobic training. The present analysis sought to determine ifV ̇O 2 maxindependently influences thermoregulatory sweating, maximum skin wettedness (ω max ) and the change in rectal temperature (Δ T re ) during 60 min of exercise in an uncompensable environment (37.0 ± 0.8°C, 4.0 ± 0.2 kPa, 64 ± 3% relative humidity) at a fixed rate of heat production per unit mass (6 W kg −1 ). Retrospective analyses were performed on 22 participants (3 groups), aerobically unfit (UF; n = 7;V ̇O 2 max: 41.7 ± 9.4 ml kg −1 min −1 ), aerobically fit (F; n = 7;V ̇O 2 max: 55.6 ± 4.3 ml kg −1 min −1 ; P < 0.01) and aerobically unfit ( n = 8) individuals, before (pre;V ̇O 2 max: 45.8 ± 11.6 ml kg −1 min −1 ) and after (post;V ̇O 2 max: 52.0 ± 11.1 ml kg −1 min −1 ; P < 0.001) an 8‐week training intervention. ω max was similar between UF (0.74 ± 0.09) and F (0.78 ± 0.08, P = 0.22). However, ω max was greater post‐ (0.84 ± 0.08) compared to pre‐ (0.72 ± 0.06, P = 0.02) training. During exercise, mean local sweat rate (forearm and upper‐back) was greater post‐ (1.24 ± 0.20 mg cm −2 min −1 ) compared to pre‐ (1.04 ± 0.25 mg cm −2 min −1 , P < 0.01) training, but similar between UF (0.94 ± 0.31 mg cm −2 min −1 , P = 0.90) and F (1.02 ± 0.30 mg cm −2 min −1 ). The Δ T re at 60 min of exercise was greater pre‐ (1.13 ± 0.16°C, P < 0.01) compared to post‐ (0.96 ± 0.14°C) training, but similar between UF (0.85 ± 0.29°C, P = 0.22) and F (0.95 ± 0.22°C). Taken together, aerobic training, notV ̇O 2 maxper se , confers an increased ω max , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals.