This study determines the effects of increasing forces on different musculoskeletal load parameters, such as muscle activity and joint movement, during assembly task-related dynamic hand strikes and isometric push forces. Fifteen subjects (12 men and 3 women) were instructed to strike and push on a force plate in two selected conditions. In the first condition, the palmar surface of the dominant hand is oriented horizontal to the measuring surface; in the second condition, the body position is maintained, but the hand is turned 90° to allow the use of the ulnar side of the hand (fist strike position). The subjects accomplished four force levels in ascending order (i.e., 150, 250, 350, and 400 N) within the corresponding striking and pushing conditions. The extracted kinematic variables of interest were strike velocity, recoil velocity, force plate contact time, peak vertical reaction force component (force plate), force impulse, muscle activity, and maximum joint ranges of motion during the push or strike process. Differences in the results between pushes and strikes and, under certain circumstances, between fist and palm strikes were identified. Increasing push forces correlate with the muscle activity in the pectoralis and lower arm extensor muscles. The fact that, at push forces > 250 N, the subjects modify and adapt their upper body and arm posture to achieve the required force could reveal an obvious feasibility limit and explain why assembly workers tend to use their hands as a hammer.

中文翻译：

---

组装任务中动态手击和等距手推上肢负荷差异的生物力学研究

本研究确定了在与装配任务相关的动态手部撞击和等长推力期间，增加力量对不同肌肉骨骼负荷参数（例如肌肉活动和关节运动）的影响。15 名受试者（12 名男性和 3 名女性）被要求在两种选定的条件下敲击和推动测力台。在第一种情况下，惯用手的手掌面与测量面平行；在第二种情况下，保持身体姿势，但将手转动 90° 以允许使用手的尺侧（拳打位置）。受试者在相应的打击和推动条件下按升序完成了四个力级别（即 150、250、350 和 400 N）。提取的感兴趣的运动学变量是打击速度、反冲速度、测力板接触时间、峰值垂直反作用力分量（测力板）、力脉冲、肌肉活动以及推动或打击过程中的最大关节运动范围。确定了推动和打击之间以及在某些情况下拳头和手掌打击之间的结果差异。增加的推力与胸大肌和下臂伸肌的肌肉活动相关。事实上，在推力 > 250 N 时，受试者会修改和调整他们的上身和手臂姿势以达到所需的力量，这可能揭示出明显的可行性限制并解释为什么装配工人倾向于将手用作锤子。确定了推动和打击之间以及在某些情况下拳头和手掌打击之间的结果差异。增加的推力与胸大肌和下臂伸肌的肌肉活动相关。事实上，在推力 > 250 N 时，受试者会修改和调整他们的上身和手臂姿势以达到所需的力量，这可能揭示出明显的可行性限制并解释为什么装配工人倾向于将手用作锤子。确定了推动和打击之间以及在某些情况下拳头和手掌打击之间的结果差异。增加的推力与胸大肌和下臂伸肌的肌肉活动相关。事实上，在推力 > 250 N 时，受试者会修改和调整他们的上身和手臂姿势以达到所需的力量，这可能揭示出明显的可行性限制并解释为什么装配工人倾向于将手用作锤子。