Department of Life Sciences, University of Roehampton, UK.
Department of Life Sciences, University of Roehampton, UK.
J Sci Med Sport. 2021 Aug;24(8):811-817. doi: 10.1016/j.jsams.2021.03.007. Epub 2021 Mar 19.
To investigate the effect of progressive whole-body hyperthermia on maximal, and rapid voluntary torque production, and their neuromuscular determinants.
Repeated measures, randomised.
Nine participants performed sets of neuromuscular assessments in HOT conditions (∼50°C, ∼35% relative humidity) at rectal temperatures (T) of 37, 38.5 and 39.5°C and in CON conditions (∼22°C, ∼35% relative humidity) at a T of ∼37°C and pre-determined comparative time-points. Electrically evoked twitch (single impulse) and octet (8 impulses at 300Hz) responses were measured at rest. Maximum voluntary torque (MVT), surface electromyography (EMG) normalised to maximal M-wave, and voluntary activation (VA) were measured during 3-5s isometric maximal voluntary contractions. Rate of torque development (RTD) and normalised EMG were measured during rapid voluntary isometric contractions from rest.
All neuromuscular variables were unaffected by time in CON. In HOT, MVT, normalised EMG at MVT and VA were lower at 39.5°C compared to 37°C (p<0.05). Early- (0-50ms) and middle- (50-100ms) phase voluntary RTD were unaffected by increased T (p>0.05), despite lower normalised EMG at T 39.5°C (p<0.05) in rapid contractions. In contrast, late-phase (100-150ms) voluntary RTD was lower at 38.5°C and 39.5°C compared to 37°C (p<0.05) in HOT. Evoked twitch and octet RTD increased with increased T (p<0.05).
Hyperthermia reduced late-phase voluntary RTD, likely due to reduced neural drive and the reduction in MVT. In contrast, early- and middle-phase voluntary RTD were unaffected by hyperthermia, likely due to the conflicting effects of reduced neural drive but faster intrinsic contractile properties.
研究全身逐渐升温对最大和快速自主扭矩产生及其神经肌肉决定因素的影响。
重复测量，随机。
9 名参与者在 HOT 条件（约 50°C，约 35%相对湿度）下直肠温度（T）为 37、38.5 和 39.5°C，以及在 CON 条件（约 22°C，约 35%相对湿度）下 T 为约 37°C 和预定的比较时间点进行神经肌肉评估。在休息时测量电诱发的 twitch（单脉冲）和 octet（300Hz 时的 8 个脉冲）反应。在 3-5s 等长最大自主收缩期间测量最大自主扭矩（MVT）、表面肌电图（EMG）归一化为最大 M 波，以及自主激活（VA）。在从休息开始的快速自主等长收缩期间测量扭矩发展速率（RTD）和归一化 EMG。
CON 条件下，所有神经肌肉变量均不受时间影响。在 HOT 中，与 37°C 相比，39.5°C 时 MVT、MVT 时归一化 EMG 和 VA 较低（p<0.05）。尽管在快速收缩时 T 为 39.5°C 时归一化 EMG 较低（p<0.05），但早期（0-50ms）和中期（50-100ms）自主 RTD 不受 T 增加的影响（p>0.05）。相比之下，在 HOT 中，与 37°C 相比，38.5°C 和 39.5°C 时晚期（100-150ms）自主 RTD 较低（p<0.05）。诱发的 twitch 和 octet RTD 随 T 增加而增加（p<0.05）。
体温升高降低了晚期自主 RTD，可能是由于神经驱动减少和 MVT 降低所致。相比之下，早期和中期自主 RTD 不受体温升高的影响，可能是由于神经驱动减少和内在收缩特性更快之间的冲突影响所致。
