THE BIOMECHANICS OF OCCUPATIONAL SHOULDER INJURIES

尽管国家职业安全与健康研究所(NIOSH)已经确定了重复手臂运动和工作场所肩部疾病之间的明确流行病学联系，但关于这种联系的生物力学方面的科学数据很少。考虑到职业性肩部疾患在美国每年有40亿美元的直接医疗费用，这是令人惊讶的。有证据表明，重复运动与肌肉疲劳和肩部异常运动有关，这反过来可能会导致肩袖肌肉系统的损害。基于这一观察，这项研究提案的总体目标是开发一个与重复的手臂运动和肩胛骨运动学改变相关的简单的肌肉疲劳指数。更具体地说，第一个具体目标是确定重复的手臂运动是否会导致肩部运动学改变。假设在重复的手臂运动过程中肩胛肌的疲劳会导致肩胛骨运动的减少。第二个具体目标是确定一个疲劳指数来解释重复运动引起的运动学变化。基于肌肉肌电频率分量的疲劳指数已被证明是下背部肌肉损伤的一个很好的预测指标。这是假设，肩胛肌的类似指标将与重复运动后肩胛骨运动学的改变相关。这些假设将通过让没有肩部病变的健康志愿者进行模拟工作活动来检验，直到他们疲惫不堪。根据NIOSH的研究结果，这将是一个高重复和低负载的活动。运动学将用磁力跟踪装置进行测量，该装置已被发现对测量肩胛骨运动既可靠又准确。疲劳敏感性将通过先前确定的肌肉疲劳指数来确定。这项提议是朝着开发一种筛查工具迈出的第一步，该工具用于评估个人抵抗重复运动的潜在有害后果的能力。最终，这些信息将被用来制定修改工作任务的策略，以及为从事高风险活动的工人制定条件计划。

Although the National Institute of Occupational Safety and Health (NIOSH) has identified a clear epidemiological link between repetitive arm motion and shoulder disorders in the workplace, there are few scientific data available regarding the biomechanics of this connection. This is surprising considering that occupational shoulder disorders have a direct medical cost of 4 billion dollars annually in the United States. There is evidence that repetitive motion is associated with muscle fatigue and abnormal shoulder motion, which in turn may lead to damage of the rotator cuff musculature. Based on this observation, the overall objective of this research proposal is to develop a simple index of muscle fatigue that is associated with repetitive arm motion and altered scapular kinematics. More specifically, the first specific aim is to determine if repetitive arm motion will lead to altered shoulder kinematics. It is hypothesized that fatigue of the scapular muscles during a repetitive arm motion will result in a decrease in scapular motion. The second specific aim is to identify a fatigue index to explain altered kinematics with repetitive motions. A fatigue index based on a muscle's EMG frequency components has been shown to be a good predictor of muscle impairment for low back muscles. It is hypothesized that a similar index for scapular muscles will be associated with alterations in scapular kinematics after repetitive motion. These hypotheses will be tested by having healthy volunteers with no shoulder pathologies perform a simulated work activity until they are fatigued. Based on the findings of NIOSH, this will be a high repetition and low load activity. Kinematics will be measured with a magnetic tracking device that has been found to be both reliable and accurate for measuring scapular motion. Fatigue susceptibility will be identified with a previously established muscle fatigue index. This proposal represents the first step towards developing a screening tool for assessing an individual's ability to resist the potentially harmful consequences of repetitive motion. Ultimately, this information will be used to develop both strategies for modifying work tasks, as well as conditioning programs for workers performing high risk activities.