Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712, USA.
Exp Brain Res. 2011 Apr;209(4):525-36. doi: 10.1007/s00221-011-2580-8. Epub 2011 Feb 18.
Performing repetitive manual tasks can lead to muscle fatigue, which may induce changes in motor coordination, movement stability, and kinematic variability. In particular, movements performed at or above shoulder height have been associated with increased shoulder injury risk. The purpose of this study was to determine the effects of repetitive motion-induced muscle fatigue on posture and on the variability and stability of upper extremity movements. Ten healthy subjects performed a repetitive task similar to sawing continuously until volitional exhaustion. This task was synchronized with a metronome to control movement timing. Subjects performed the sawing task at shoulder ("High") and sternum height ("Low") on two different days. Joint angles and muscle activity were recorded continuously. Local and orbital stability of joint angles, kinematic variability (within subject standard deviations), and peak joint angles were calculated for five bins of data spaced evenly across each trial. Subjects fatigued more quickly when movements were performed at the High height. They also altered their kinematic patterns significantly in response to muscle fatigue. These changes were more pronounced when the task was performed at the High height. Subjects also exhibited increased kinematic variability of their movements post-fatigue. Increases in variability and altered coordination did not lead to greater instability, however. Shoulder movements were more locally stable when the task was performed at the High height. Conversely, shoulder and elbow movements were more orbitally unstable for the High condition. Thus, people adapt their movement strategies in multi-joint redundant tasks and maintain stability in doing so.
进行重复性的手工任务可能会导致肌肉疲劳，从而导致运动协调、运动稳定性和运动学可变性发生变化。特别是在肩高或以上进行的运动与增加肩部受伤风险有关。本研究的目的是确定重复运动引起的肌肉疲劳对姿势以及上肢运动的可变性和稳定性的影响。 10 名健康受试者连续进行类似于锯切的重复任务，直到自愿力竭。该任务与节拍器同步，以控制运动时间。受试者在两天内在两个不同的位置（肩部“高”和胸骨“低”）进行锯切任务。连续记录关节角度和肌肉活动。为每个试验均匀间隔的五个数据箱计算关节角度的局部和轨道稳定性、运动学可变性（个体内标准差）和峰值关节角度。当运动在高位置进行时，受试者疲劳得更快。他们还根据肌肉疲劳显著改变了他们的运动模式。当任务在高位置进行时，这些变化更加明显。受试者在疲劳后也表现出运动的运动学可变性增加。然而，可变性和协调改变并没有导致更大的不稳定性。当任务在高位置进行时，肩部运动的局部稳定性更高。相反，肩部和肘部运动在高条件下的轨道稳定性较低。因此，人们在多关节冗余任务中调整他们的运动策略，并在这样做的过程中保持稳定性。
