Proximal and distal muscle fatigue differentially affect movement coordination

Muscle fatigue can cause people to change their movement patterns and these changes could contribute to acute or overuse injuries. However, these effects depend on which muscles are fatigued. The purpose of this study was to determine the differential effects of proximal and distal upper extremity muscle fatigue on repetitive movements. Fourteen subjects completed a repetitive ratcheting task before and after a fatigue protocol on separate days. The fatigue protocol either fatigued the proximal (shoulder flexor) or distal (finger flexor) muscles. Pre/Post changes in trunk, shoulder, elbow, and wrist kinematics were compared to determine how proximal and distal fatigue affected multi-joint movement patterns and variability. Proximal fatigue caused a significant increase (7°, p < 0.005) in trunk lean and velocity, reduced humeral elevation (11°, p < 0.005), and increased elbow flexion (4°, p < 0.01). In contrast, distal fatigue caused small but significant changes in trunk angles (2°, p < 0.05), increased velocity of wrench movement relative to the hand (17°/s, p < 0.001), and earlier wrist extension (4%, p < 0.005). Movement variability increased at proximal joints but not distal joints after both fatigue protocols (p < 0.05). Varying movements at proximal joints may help people adapt to fatigue at either proximal or distal joints. The identified differences between proximal and distal muscle fatigue adaptations could facilitate risk assessment of occupational tasks.

肌肉疲劳可导致个体改变运动模式，此类改变可能诱发急性损伤或过度使用性损伤。然而，此类影响取决于疲劳发生的肌肉部位。本研究旨在探究上肢近端与远端肌肉疲劳对重复性运动的差异化影响。十四名受试者分别在不同日期完成疲劳干预前后的重复性棘轮（ratcheting）任务。本次疲劳干预方案分别针对近端肌肉（肩关节屈肌）或远端肌肉（指屈肌）进行疲劳诱导。研究对躯干、肩关节、肘关节及腕关节的运动学（kinematics）参数在干预前后的变化进行对比，以明确近端与远端肌肉疲劳如何影响多关节运动模式及其变异性。近端肌肉疲劳可导致躯干倾斜角度及运动速度显著升高（7°，p < 0.005），同时降低肱骨抬高角度（11°，p < 0.005），并增加肘关节屈曲角度（4°，p < 0.01）。与之相对，远端肌肉疲劳仅引发躯干角度出现小幅但显著的变化（2°，p < 0.05），同时提升了扳手相对于手部的运动速度（17°/s，p < 0.001），并使腕关节伸展时机提前（4%，p < 0.005）。两种疲劳干预方案实施后，近端关节的运动变异性均出现升高，而远端关节则无显著变化（p < 0.05）。通过调整近端关节的运动模式，个体或可适应近端或远端肌肉疲劳带来的影响。本研究明确的近端与远端肌肉疲劳适应性差异，可为职业任务的风险评估提供辅助支撑。