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Hyperthermia reduces electromechanical delay via accelerated electrochemical processes

Abstract : The present study aimed to determine the effect of hyperthermia on both electrochemical and mechanical components of the electromechanical delay (EMD), using very-high-frame-rate ultrasound. Electrically evoked peak twitch force, EMD, electrochemical (D m ; i.e., delay between stimulation and muscle fascicle motion), and mechanical (T m ; i.e., delay between fascicle motion and force production onset) components of EMD were assessed in 16 participants. Assessments were conducted in a control ambient environment (CON; 26 C, 34% relative humidity) and in a hot ambient environment (HOT; 46-50 C, 18% relative humidity, after $127 min of heat exposure). Following heat exposure, gastrocnemius medialis temperature was 37.0 ± 0.6 C in HOT vs. 34.0 ± 0.8 C in CON (P < 0.001). EMD was shorter (9.4 ± 0.8 ms) in HOT than in CON (10.8 ± 0.6 ms, P < 0.001). Electrochemical processes were shorter in HOT than in CON (4.0 ± 0.8 ms vs. 5.5 ± 0.9 ms, respectively, P < 0.001), whereas mechanical processes were unchanged (P = 0.622). These results demonstrate that hyperthermia reduces electromechanical delay via accelerated electrochemical processes, whereas force transmission along the active and passive parts of the series elastic component is not affected following heat exposure. The present study demonstrates that heat exposure accelerates muscle contraction thanks to faster electrochemical processes. Further investigations during voluntary contractions would contribute to better understand how these findings translate into motor performance. NEW & NOTEWORTHY Hyperthermia (targeted core temperature: 38.5 C) reduces the time between gastrocnemius medialis stimulation and the onset of plantar flexor force production in vivo. This reduction in electromechanical delay is concomitant to an earlier motion of muscle fascicle compared with thermoneutral environment. However, hyperthermia has no impact on the duration of force transmission along aponeurosis and tendon, thereby reflecting different effects of heat exposure on contractile and elastic properties of the muscle-tendon unit.
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https://hal.archives-ouvertes.fr/hal-03466475
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Soumis le : mercredi 22 décembre 2021 - 20:20:41
Dernière modification le : vendredi 22 avril 2022 - 15:50:02
Archivage à long terme le : : mercredi 23 mars 2022 - 18:02:16

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Adèle Mornas, Sébastien Racinais, Franck Brocherie, Marine Alhammoud, Robin Hager, et al.. Hyperthermia reduces electromechanical delay via accelerated electrochemical processes. Journal of Applied Physiology, American Physiological Society, 2021, 130, pp.290 - 297. ⟨10.1152/japplphysiol.00538.2020⟩. ⟨hal-03466475⟩

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