Mohr Maurice, Nann Marius, von Tscharner Vinzenz, Eskofier Bjoern, Nigg Benno Maurus
Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada; Biomechanigg Sport & Health Research Inc., Calgary, Alberta, Canada.
Digital Sports Group, Friedrich-Alexander University Erlangen-Nuernberg, Erlangen, Germany.
PLoS One. 2015 Nov 3;10(11):e0142048. doi: 10.1371/journal.pone.0142048. eCollection 2015.
Motor unit activity is coordinated between many synergistic muscle pairs but the functional role of this coordination for the motor output is unclear. The purpose of this study was to investigate the short-term modality of coordinated motor unit activity-the synchronized discharge of individual motor units across muscles within time intervals of 5ms-for the Vastus Medialis (VM) and Lateralis (VL). Furthermore, we studied the task-dependency of intermuscular motor unit synchronization between VM and VL during static and dynamic squatting tasks to provide insight into its functional role.
Sixteen healthy male and female participants completed four tasks: Bipedal squats, single-leg squats, an isometric squat, and single-leg balance. Monopolar surface electromyography (EMG) was used to record motor unit activity of VM and VL. For each task, intermuscular motor unit synchronization was determined using a coherence analysis between the raw EMG signals of VM and VL and compared to a reference coherence calculated from two desynchronized EMG signals. The time shift between VM and VL EMG signals was estimated according to the slope of the coherence phase angle spectrum.
For all tasks, except for singe-leg balance, coherence between 15-80Hz significantly exceeded the reference. The corresponding time shift between VM and VL was estimated as 4ms. Coherence between 30-60Hz was highest for the bipedal squat, followed by the single-leg squat and the isometric squat.
There is substantial short-term motor unit synchronization between VM and VL. Intermuscular motor unit synchronization is enhanced for contractions during dynamic activities, possibly to facilitate a more accurate control of the joint torque, and reduced during single-leg tasks that require balance control and thus, a more independent muscle function. It is proposed that the central nervous system scales the degree of intermuscular motor unit synchronization according to the requirements of the movement task at hand.
运动单位活动在许多协同肌对之间是协调的，但这种协调对运动输出的功能作用尚不清楚。本研究的目的是调查股内侧肌（VM）和股外侧肌（VL）之间协调运动单位活动的短期模式——在5毫秒时间间隔内各运动单位跨肌肉的同步放电。此外，我们研究了在静态和动态深蹲任务期间VM和VL之间肌间运动单位同步的任务依赖性，以深入了解其功能作用。
16名健康男性和女性参与者完成了四项任务：双脚深蹲、单腿深蹲、等长深蹲和单腿平衡。使用单极表面肌电图（EMG）记录VM和VL的运动单位活动。对于每项任务，使用VM和VL原始EMG信号之间的相干分析确定肌间运动单位同步，并与从两个去同步EMG信号计算出的参考相干进行比较。根据相干相位角谱的斜率估计VM和VL EMG信号之间的时间延迟。
对于所有任务，除了单腿平衡外，15 - 80Hz之间的相干显著超过参考值。VM和VL之间的相应时间延迟估计为4毫秒。30 - 60Hz之间的相干在双脚深蹲时最高，其次是单腿深蹲和等长深蹲。
VM和VL之间存在显著的短期运动单位同步。在动态活动期间，肌间运动单位同步在收缩时增强，可能是为了促进对关节扭矩的更精确控制，而在需要平衡控制从而需要更独立肌肉功能的单腿任务中则降低。有人提出，中枢神经系统根据手头运动任务的要求调整肌间运动单位同步的程度。
