PDF(Pubmed)
Abstract：
Background: We investigated the impact of 1) passive heating (PH) induced by single and intermittent/prolonged hot-water immersion (HWI) and 2) the duration of PH, on muscle contractile function under the unfatigued state, and during the development of muscle fatigue. Methods: Twelve young males volunteered for this study consisting of two phases: single phase (SP) followed by intermittent/prolonged phase (IPP), with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and HWI (44-45°C; water up to the waist level). SP-HWI included one continuous 45-min bath (from 15 to 60 min). IPP-HWI included an initial 45-min bath (from 15 to 60 min) followed by eight additional 15-min baths interspaced with 15-min breaks at room temperature between 75 and 300 min. Intramuscular (Tmu; measured in the vastus lateralis muscle) and rectal (Trec) temperatures were determined. Neuromuscular testing (performed in the knee extensors and flexors) was performed at baseline and 60 min later during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations of the knee extensors) was performed after the last neuromuscular testing of each trial. Results: HWI increased Tmu and Trec to 38°C-38.5°C (p < 0.05) during both SP and IPP. Under the unfatigued state, HWI did not affect electrically induced torques at 20 Hz (P20) and 100 Hz (P100). However, it induced a shift towards a faster contractile profile during both SP and IPP, as evidenced by a decreased P20/P100 ratio (p < 0.05) and an improved muscle relaxation (i.e., reduced half-relaxation time and increased rate of torque relaxation; p < 0.05). Despite a reduced voluntary activation (i.e., -2.63% ± 4.19% after SP-HWI and -5.73% ± 4.31% after IPP-HWI; condition effect: p < 0.001), HWI did not impair maximal isokinetic and isometric contraction torques. During the fatiguing protocol, fatigue index and the changes in muscle contractile properties were larger after HWI than CON conditions (p < 0.05). Finally, none of these parameters were significantly affected by the heating duration. Conclusion: PH induces changes in muscle contractile function which are not augmented by prolonged exposure when thermal stress is moderate.
摘要：
背景：我们调查了1）单次和间歇性/长时间热水浸泡（HWI）引起的被动加热（PH）和2）PH持续时间的影响，在不疲劳状态下的肌肉收缩功能，在肌肉疲劳的发展过程中。方法：12名年轻男性自愿参加本研究，包括两个阶段：单相（SP），然后是间歇性/延长时间（IPP）。两个阶段都包括两个条件(即，总共四项试验）随机进行：对照被动坐姿（CON）和HWI（44-45°C；水至腰部水平）。SP-HWI包括一个连续45分钟的浴(从15至60分钟)。IPP-HWI包括初始45分钟的浴（15至60分钟），然后是8个额外的15分钟浴，在室温下在75至300分钟之间间隔15分钟。确定肌内（Tmu；在股外侧肌中测量）和直肠（Trec）温度。神经肌肉测试（在膝盖伸肌和屈肌中进行）在基线和60分钟后在SP期间进行，在基线，在IPP期间基线后60、90、150和300分钟。在每次试验的最后一次神经肌肉测试后，进行疲劳方案（对膝盖伸肌进行100次电刺激）。结果：在SP和IPP期间，HWI将Tmu和Trec升高至38°C-38.5°C（p<0.05）。在不疲劳的状态下，HWI在20Hz(P20)和100Hz(P100)下不影响电诱导扭矩。然而,在SP和IPP期间，它诱导了向更快的收缩曲线的转变，如P20/P100比率降低(p<0.05)和肌肉松弛改善(即，半松弛时间减少，扭矩松弛率增加；p<0.05)。尽管自愿激活减少(即，SP-HWI后-2.63％±4.19％，IPP-HWI后-5.73％±4.31％；条件效果：p<0.001），HWI不会损害最大等速和等距收缩扭矩。在疲劳协议期间，HWI后的疲劳指数和肌肉收缩特性的变化大于CON条件（p<0.05）。最后,这些参数均不受加热持续时间的显着影响。结论：PH会引起肌肉收缩功能的变化，而当热应激中等时，长时间暴露不会增强这种变化。
