目的:评估在热应激条件下,下肢肌肉的快速肌肉力量/扭矩产生能力和神经肌肉活动的变化的时间过程。
方法:扭矩发展(RTD)和肌电图活动的速率(EMG;即,在膝关节伸肌(KE)和足底屈肌(PF)的短暂(3-5s)爆炸性最大等距自愿性收缩(MVC)期间,均方根)上升从0到30,-50,-100和-200ms,以及整个扭矩-时间曲线内的峰值RTD。这些值记录在12名男子网球运动员之前(赛前)和之后(赛后,24和48小时)在HOT(〜37°C)和COOL(〜22°C)条件下进行比赛。
结果:比赛后核心温度在HOT(〜39.4°C)与COOL(〜38.7°C)条件下更高(p<0.05)。KERTD的减少发生在比赛后收缩开始后的0-200ms时间内和24小时,与预匹配相比,与环境条件无关(p<0.05)。在匹配后相对于匹配前也观察到KE峰值RTD的类似降低(p<0.05)。在归一化到MVC扭矩之后,没有观察到KERTD值的差异。此外,KEEMG活性上升速率保持不变。相反,运动或环境条件不影响PF收缩RTD和EMG活性升高的速率。
结论:在KE中,长时间打网球后最大扭矩生产能力的降低似乎是扭矩发展速度降低的原因,独立于环境条件,而在PF中保持不变。
OBJECTIVE: To assess the time course of changes in rapid muscle force/torque production capacity and neuromuscular activity of lower limb muscles in response to prolonged (∼2 h) match-play tennis under heat stress.
METHODS: The rates of torque development (RTD) and electromyographic activity (EMG; ie, root mean square) rise were recorded from 0 to 30, -50, -100 and -200 ms during brief (3-5 s) explosive maximal isometric voluntary contractions (MVC) of the knee extensors (KE) and plantar flexors (PF), along with the peak RTD within the entirety of the torque-time curve. These values were recorded in 12 male tennis players before (prematch) and after (postmatch, 24 and 48 h) match-play in HOT (∼37°C) and COOL (∼22°C) conditions.
RESULTS: The postmatch core temperature was greater in the HOT (∼39.4°C) vs COOL (∼38.7°C) condition (p<0.05). Reductions in KE RTD occurred within the 0-200 ms epoch after contraction onset postmatch and at 24 h, compared with prematch, independent of environmental conditions (p<0.05). A similar reduction in the KE peak RTD was also observed postmatch relative to prematch (p<0.05). No differences in KE RTD values were observed after normalisation to MVC torque. Furthermore, the rate of KE EMG activity rise remained unchanged. Conversely, the PF contractile RTD and rate of EMG activity rise were unaffected by the exercise or environmental conditions.
CONCLUSIONS: In the KE, a reduction in maximal torque production capacity following prolonged match-play tennis appears to account for the decrease in the rate of torque development, independent of environmental conditions, while remaining unchanged in the PF.