Sheikhzadeh Ali, Parnianpour Mohamad, Nordin Margareta
The Occupational and Industrial Orthopaedic Center and Program of Ergonomics and Biomechanics, New York University, NYU Hospital for Joint Diseases, 63 Downing Street, New York, NY 10014, USA.
Clin Biomech (Bristol). 2008 Jun;23(5):527-35. doi: 10.1016/j.clinbiomech.2007.11.017. Epub 2008 Jan 22.
Work-related risk factors of low back disorders have been identified to be external moments, awkward postures, and asymmetrical dynamic lifting amongst others. The distinct role of asymmetry of load versus posture is hard to discern from the literature. Hence, the aim of this study is to measure isometric trunk exertions at upright standing posture at different exertion level and degree of asymmetry to further delineate the effects of exertion level and asymmetry on neuromuscular capability response.
Fifteen healthy volunteers randomly performed trunk exertions at three levels (30%, 60%, and 100% of maximum voluntary exertion and five different angles (0 degrees , 45 degrees , 90 degrees , 135 degrees , and 180 degrees ) of normalized resultant moments. During each trial, the normalized EMG activity of 10 selected trunk muscles was quantified.
The EMG activity of the 10 trunk muscles was significantly (P<0.001) affected by the level of exertion and angle of normalized resultant moment, and their interactions. The controllability of the torque generation was reduced in biaxial exertions. The capability to generate and control the required trunk moments is significantly lowered during biaxial trunk exertions, while all muscles present higher EMG activity. These results suggest that the trunk muscles will be taxed higher while performing biaxial exertion tasks, increasing muscle fatigue possibly leading to a higher probability of low back injury.
The prediction of biaxial trunk performance based on uniaxial data will result in an overestimation of capability and controllability of the trunk during physically demanding tasks. This study provides a better understanding of the potential mechanisms of injury during asymmetrical and biaxial trunk exertion during work-related tasks.
已确定与工作相关的下背部疾病风险因素包括外部力矩、不良姿势以及不对称动态提举等。从文献中很难辨别负荷不对称与姿势不对称的不同作用。因此，本研究的目的是测量在不同用力水平和不对称程度下直立站立姿势时的等长躯干用力，以进一步阐明用力水平和不对称对神经肌肉能力反应的影响。
15名健康志愿者随机在三个水平（最大自主用力的30%、60%和100%）和五个不同角度（0度、45度、90度、135度和180度）的归一化合成力矩下进行躯干用力。在每次试验中，对10块选定的躯干肌肉的归一化肌电图活动进行量化。
10块躯干肌肉的肌电图活动受用力水平、归一化合成力矩角度及其相互作用的显著影响（P<0.001）。双轴用力时扭矩产生的可控性降低。在双轴躯干用力期间，产生和控制所需躯干力矩的能力显著降低，而所有肌肉的肌电图活动均较高。这些结果表明，在进行双轴用力任务时，躯干肌肉将承受更高的负荷，增加肌肉疲劳，可能导致下背部受伤的可能性更高。
基于单轴数据预测双轴躯干性能会导致在体力要求较高的任务中高估躯干的能力和可控性。本研究有助于更好地理解与工作相关任务中不对称和双轴躯干用力期间受伤的潜在机制。
