Evaluation of the maximum voluntary isometric lumbar extension in three-dimensional positions

Objective. Asymmetrical trunk positions to perform daily tasks are known as risk factors for back injuries. This study aimed to investigate the lumbar extension (main activity for lifting) in symmetrical, asymmetrical and combined positions. Methods. Sixteen lumbar and abdominal muscle activities during maximum voluntary contraction in six main directions and the isometric extension in 24 different positions were recorded for 14 healthy men. The co-contraction index was calculated between all the muscle pairs for each trial (120 pairs per trial). The relationship between uniaxial and combined positions was investigated using Pearson’s correlation and the response surface methodology model. Results. Pearson’s correlation between the combined positions and extension was 0.482–0.588 and for the other five main directions was Conclusions. Secondary activities due to asymmetrical position reduce the subject ability to apply maximum extension. The optimal asymmetrical lifting mode is when it is accompanied by flexion and avoids side bending as much as possible. To reduce back injuries, and increase ergonomics and occupational safety, the work environment should be designed in such a way that the spine is not exposed to excessive loads.研究目的：日常生活任务中采取的躯干不对称姿势，已被证实为腰背损伤的危险因素。本研究旨在探究对称、不对称及复合姿势下的腰椎伸展动作（提举动作的核心活动）相关特征。 研究方法：纳入14名健康男性受试者，记录其在6个主要方向的最大自主收缩（maximum voluntary contraction）状态，以及24种不同姿势下的等长伸展（isometric extension）状态时，16块腰腹部肌肉的肌电活动。针对每次试验（每次试验含120对肌肉组合），计算所有肌肉对的共同收缩指数（co-contraction index）。采用皮尔逊相关分析（Pearson’s correlation）与响应面法（response surface methodology），探究单轴姿势与复合姿势间的关联。 研究结果：复合姿势与伸展动作间的皮尔逊相关系数为0.482~0.588，其余五个主要方向的相关系数暂未明确。 研究结论：不对称姿势引发的次级活动，会降低受试者完成最大伸展动作的能力。最优的不对称提举姿势模式为伴随屈曲动作，并尽可能避免侧屈。为降低腰背损伤风险、提升人机工程学水平与职业安全性，工作环境的设计应确保脊柱不会承受过度负荷。