Skip Navigation LinksHome > October 2013 - Volume 45 - Issue 10 > Muscle-Damaging Exercise Increases Heat Strain during Subseq...
Medicine & Science in Sports & Exercise:
doi: 10.1249/MSS.0b013e318294b0f8
Basic Sciences

Muscle-Damaging Exercise Increases Heat Strain during Subsequent Exercise Heat Stress

FORTES, MATTHEW BENJAMIN1; DI FELICE, UMBERTO1,2; DOLCI, ALBERTO1; JUNGLEE, NAUSHAD A.1; CROCKFORD, MICHAEL J.1; WEST, LIAM1; HILLIER-SMITH, RYAN1; MACDONALD, JAMIE HUGO1; WALSH, NEIL PETER1

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Abstract

Purpose: It remains unclear whether exercise-induced muscle damage (EIMD) increases heat strain during subsequent exercise heat stress, which in turn may increase the risk of exertional heat illness. We examined heat strain during exercise heat stress 30 min after EIMD to coincide with increases in circulating pyrogens (e.g., interleukin-6 [IL-6]) and 24 h after EIMD to coincide with the delayed muscle inflammatory response when a higher rate of metabolic energy expenditure () and thus decreased economy might also increase heat strain.

Methods: Thirteen non–heat-acclimated males (mean ± SD, age = 20 ± 2 yr) performed exercise heat stress tests (running for 40 min at 65% V˙O2max in 33°C, 50% humidity) 30 min (HS1) and 24 h (HS2) after treatment, involving running for 60 min at 65% V˙O2max on either −10% gradient (EIMD) or +1% gradient (CON) in a crossover design. Rectal (Tre) and skin (Tsk) temperature, local sweating rate, and were measured throughout HS tests.

Results: Compared with CON, EIMD evoked higher circulating IL-6 pre-HS1 (P < 0.01) and greater plasma creatine kinase and muscle soreness pre-HS2 (P < 0.01). The ΔTre was greater after EIMD than CON during HS1 (0.35°C, 95% confidence interval = 0.11°C–0.58°C, P < 0.01) and HS2 (0.17°C, 95% confidence interval = 0.07°C–0.28°C, P < 0.01). was higher on EIMD throughout HS1 and HS2 (P < 0.001). Thermoeffector responses (Tsk, sweating rate) were not altered by EIMD. Thermal sensation and RPE were higher on EIMD after 25 min during HS1 (P < 0.05). The final Tre during HS1 correlated with the pre-HS1 circulating IL-6 concentration (r = 0.67).

Conclusions: Heat strain was increased during endurance exercise in the heat conducted 30 min after and, to a much lesser extent, 24 h after muscle-damaging exercise. These data indicate that EIMD is a likely risk factor for exertional heat illness particularly during exercise heat stress when behavioral thermoregulation cues are ignored.

© 2013 American College of Sports Medicine

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