Treigyte Viktorija, Chaillou Thomas, Eimantas Nerijus, Venckunas Tomas, Brazaitis Marius
Sports Science and Innovation Institute, Lithuanian Sports University, Kaunas, Lithuania.
School of Health Sciences, Örebro University, Örebro, Sweden.
Front Physiol. 2024 Feb 27;15:1356488. doi: 10.3389/fphys.2024.1356488. eCollection 2024.
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. 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 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. HWI increased Tmu and Trec to 38°C-38.5°C ( < 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 ( < 0.05) and an improved muscle relaxation (i.e., reduced half-relaxation time and increased rate of torque relaxation; < 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: < 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 ( < 0.05). Finally, none of these parameters were significantly affected by the heating duration. PH induces changes in muscle contractile function which are not augmented by prolonged exposure when thermal stress is moderate.
1）单次及间歇性/持续性热水浸泡（HWI）引起的被动加热（PH），以及2）PH的持续时间，对未疲劳状态下以及肌肉疲劳发展过程中肌肉收缩功能的影响。12名年轻男性自愿参与本研究，研究分为两个阶段：单相（SP）阶段，随后是间歇性/持续性阶段（IPP），两个阶段均包括两种随机进行的条件（即总共四项试验）：对照被动坐姿（CON）和HWI（44 - 45°C；水深至腰部）。SP - HWI包括一次持续45分钟的浸泡（从第15分钟至60分钟）。IPP - HWI包括最初45分钟的浸泡（从第15分钟至60分钟），随后在75至300分钟之间，每隔15分钟进行一次15分钟的浸泡，并在室温下间隔15分钟休息。测定了肌肉内温度（Tmu；在肌肉中测量）和直肠温度（Trec）。在基线时以及SP阶段60分钟后，以及IPP阶段基线后60、90、150和300分钟，对膝伸肌和屈肌进行神经肌肉测试。在每项试验的最后一次神经肌肉测试后，进行疲劳方案（对膝伸肌进行100次电刺激）。在SP和IPP阶段，HWI均使Tmu和Trec升高至38°C - 38.5°C（P < 0.05）。在未疲劳状态下，HWI不影响20Hz（P20）和100Hz（P100）时的电诱发扭矩。然而，在SP和IPP阶段，它都诱导了向更快收缩模式的转变，表现为P20/P100比值降低（P < 0.05）和肌肉放松改善（即半放松时间缩短和扭矩放松速率增加；P < 0.05）。尽管自愿激活降低（即SP - HWI后降低2.63%±4.19%，IPP - HWI后降低5.73%±4.31%；条件效应：P < 0.001），但HWI并未损害最大等速和等长收缩扭矩。在疲劳方案期间，HWI条件下的疲劳指数和肌肉收缩特性变化比CON条件下更大（P < 0.05）。最后，这些参数均未受到加热持续时间的显著影响。当热应激适度时，PH会引起肌肉收缩功能的变化，长时间暴露并不会增强这种变化。
