Passive heat acclimation improves skeletal muscle contractility in humans.
Am J Physiol Regul Integr Comp Physiol
; 312(1): R101-R107, 2017 01 01.
Article
en En
| MEDLINE
| ID: mdl-27903515
The aim of this study was to investigate the effect of repeated passive heat exposure (i.e., acclimation) on muscle contractility in humans. Fourteen nonheat-acclimated males completed two trials including electrically evoked twitches and voluntary contractions in thermoneutral conditions [Cool: 24°C, 40% relative humidity (RH)] and hot ambient conditions in the hyperthermic state (Hot: 44-50°C, 50% RH) on consecutive days in a counterbalanced order. Rectal temperature was ~36.5°C in Cool and was maintained at ~39°C throughout Hot. Both trials were repeated after 11 days of passive heat acclimation (1 h per day, 48-50°C, 50% RH). Heat acclimation decreased core temperature in Cool (-0.2°C, P < 0.05), increased the time required to reach 39°C in Hot (+9 min, P < 0.05) and increased sweat rate in Hot (+0.7 liter/h, P < 0.05). Moreover, passive heat acclimation improved skeletal muscle contractility as evidenced by an increase in evoked peak twitch amplitude both in Cool (20.5 ± 3.6 vs. 22.0 ± 4.0 N·m) and Hot (20.5 ± 4.7 vs. 22.0 ± 4.0 N·m) (+9%, P < 0.05). Maximal voluntary torque production was also increased both in Cool (145 ± 42 vs. 161 ± 36 N·m) and Hot (125 ± 36 vs. 145 ± 30 N·m) (+17%, P < 0.05), despite voluntary activation remaining unchanged. Furthermore, the slope of the relative torque/electromyographic linear relationship was improved postacclimation (P < 0.05). These adjustments demonstrate that passive heat acclimation improves skeletal muscle contractile function during electrically evoked and voluntary muscle contractions of different intensities both in Cool and Hot. These results suggest that repeated heat exposure may have important implications to passively maintain or even improve muscle function in a variety of performance and clinical settings.
Palabras clave
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Regulación de la Temperatura Corporal
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Músculo Esquelético
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Respuesta al Choque Térmico
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Fuerza Muscular
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Termotolerancia
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Contracción Isométrica
Límite:
Adult
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Humans
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Male
Idioma:
En
Revista:
Am J Physiol Regul Integr Comp Physiol
Asunto de la revista:
FISIOLOGIA
Año:
2017
Tipo del documento:
Article
País de afiliación:
Qatar
Pais de publicación:
Estados Unidos