Research Group in Physical Activity and Health (GRAFiS), Institut Nacional d'Educació Física de Catalunya (INEFC), Universitat de Barcelona (UB), 08038 Barcelona, Spain.
Plymouth Institute of Health and Care Research (PIHR), University of Plymouth, Plymouth PL4 8AA, UK.
Int J Environ Res Public Health. 2021 Jul 27;18(15):7926. doi: 10.3390/ijerph18157926.
Despite a reduction in the maximal voluntary isometric contraction (MVC) observed systematically in intermittent fatigue protocols (IFP), decrements of the median frequency, assessed by surface electromyography (sEMG), has not been consistently verified. This study aimed to determine whether recovery periods of 60 s were too long to induce a reduction in the normalized median frequency (MF) of the flexor digitorum superficialis and carpi radialis muscles. Twenty-one road racing motorcycle riders performed an IFP that simulated the posture and braking gesture on a motorcycle. The MVC was reduced by 53% ( < 0.001). A positive and significant relationship ( < 0.005) was found between MF and duration of the fatiguing task when 5 s contractions at 30% MVC were interspersed by 5 s recovery in both muscles. In contrast, no relationship was found ( > 0.133) when 10 s contractions at 50% MVC were interspersed by 1 min recovery. Comparative analysis of variance (ANOVA) confirmed a decrement of MF in the IFP at 30% MVC including short recovery periods with a duty cycle of 100% (5 s/5 s = 1), whereas no differences were observed in the IFP at 50% MVC and longer recovery periods, with a duty cycle of 16%. These findings show that recovery periods during IFP are more relevant than the intensity of MVC. Thus, we recommend the use of short recovery periods between 5 and 10 s after submaximal muscle contractions for specific forearm muscle training and testing purposes in motorcycle riders.
尽管在间歇性疲劳方案（IFP）中系统地观察到最大等长收缩（MVC）的减少，但表面肌电图（sEMG）评估的中值频率的减少并未得到一致验证。本研究旨在确定 60 秒的恢复期是否过长，以至于无法降低指浅屈肌和桡侧腕屈肌的归一化中值频率（MF）。21 名公路赛车摩托车骑手进行了 IFP，模拟了摩托车上的姿势和制动手势。MVC 降低了 53%（<0.001）。当以 30%MVC 进行 5 秒收缩，然后以 5 秒恢复的方式在两块肌肉中插入 5 秒收缩时，MF 与疲劳任务的持续时间之间存在正相关（<0.005）。相比之下，当以 50%MVC 进行 10 秒收缩，然后以 1 分钟恢复的方式插入时，未发现相关性（>0.133）。比较方差分析（ANOVA）证实，在 30%MVC 的 IFP 中，包括具有 100%占空比（5 s/5 s=1）的短恢复期，MF 会降低，而在 50%MVC 的 IFP 中，MF 则没有差异，且恢复时间更长，占空比为 16%。这些发现表明，在 IFP 期间的恢复期比 MVC 的强度更重要。因此，我们建议在摩托车骑手进行特定前臂肌肉训练和测试时，在亚最大肌肉收缩后使用 5 到 10 秒的短恢复期。
