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Eur J Appl Physiol. 2012 Oct;112(10):3569-76. doi: 10.1007/s00421-012-2336-6. Epub 2012 Feb 10.

Influence of passive lower-body heating on muscle metabolic perturbation and high-intensity exercise tolerance in humans.

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1
Sport and Health Sciences, College of Life and Environmental Sciences, Exeter, UK.

Abstract

The purpose of this investigation was to determine the influence of heat stress on the dynamics of muscle metabolic perturbation during high-intensity exercise. Seven healthy males completed single-legged knee-extensor exercise until the limit of tolerance on two separate occasions. In a randomized order the subjects underwent 40 min of lower-body immersion in warm water at 42°C prior to exercise (HOT) or received no prior thermal manipulation (CON). Following the intervention, muscle metabolism was measured at rest and throughout exercise using (31)P-MRS. The tolerable duration of high-intensity exercise was reduced by 36% after passive heating (CON: 474 ± 146 vs. HOT: 303 ± 76 s; P = 0.005). Intramuscular pH was lower over the first 60 s of exercise (CON: 7.05 ± 0.02 vs. HOT: 7.00 ± 0.03; P = 0.019) in HOT compared to CON. The rate of muscle [PCr] degradation during exercise was greater in the HOT condition (CON: -0.17 ± 0.08 vs. HOT: -0.25 ± 0.10% s(-1); P = 0.006) and pH also tended to change more rapidly in HOT (P = 0.09). Muscle [PCr] (CON: 26 ± 14 vs. HOT: 29 ± 10%), [Pi] (CON: 504 ± 236 vs. HOT: 486 ± 186%) and pH (CON: 6.84 ± 0.13 vs. HOT: 6.80 ± 0.14; P > 0.05) were not statistically different at the limit of tolerance (P > 0.05 for all comparisons). These results suggest that the reduced time-to-exhaustion during high-intensity knee-extensor exercise following lower-body heating might be related, in part, to accelerated rates of change of intramuscular [PCr] and pH towards 'critical' values that limit muscle function.

PMID:
22323297
DOI:
10.1007/s00421-012-2336-6
[Indexed for MEDLINE]

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