van der Helm F C, Veeger H E
Department of Mechanical Engineering and Marine Technology, Delft University of Technology, Netherlands.
J Biomech. 1996 Jan;29(1):39-52. doi: 10.1016/0021-9290(95)00026-7.
During wheelchair propulsion the largest net joint moments and net joint powers are generated around the shoulder. The analysis of the contribution of arm- and shoulder muscles to the joint moments could explain the low efficiency of wheelchair propulsion. Basically, it is assumed that a large magnitude of muscle activity will be needed to stabilize the shoulder. In addition, the muscular requirements for the minimization of negative power are assumed to be of importance. For such an analysis an inverse dynamic model is required. To utilize an inverse dynamic model of the shoulder mechanism, the trajectories of the upper extremity bones are needed. Since at this stage, dynamic non-invasive measurement techniques of scapular motion are not available, the aim of this study was to record the three-dimensional position of the scapula in static situations with the help of a palpation technique. Positions of the trunk, shoulder girdle and upper extremity, and the surface EMG of ten muscles were recorded simultaneously with forces on the rim on a stationary wheelchair ergometer. Four healthy male subjects participated in the experiment. Five hand positions on the rim and five different load levels per hand position were measured for each subject. A previously developed musculoskeletal model of the shoulder mechanism (Van der Helm, 1994a, J. Biomechanics 27(5) 551-569) was used to calculate muscle forces in an inverse static simulation. The measured EMG and the calculated muscle forces compared well except for three muscles. The moment balance between external sources and muscles around each joint axis of the shoulder mechanism is discussed. Results of the experiment indicate that large muscle contributions are needed for joint stabilization. The experimental results on the scapular motions will, in combination with experimental data collected under dynamic conditions, be used for application of the model to dynamic situations. It is concluded that the musculoskeletal model of the shoulder mechanism can be very useful in studies to determine the contribution of muscles and the mechanical load on morphological structures.
在轮椅推进过程中，最大的净关节力矩和净关节功率产生于肩部周围。分析手臂和肩部肌肉对关节力矩的贡献，有助于解释轮椅推进效率低下的原因。基本上，可以认为需要大量的肌肉活动来稳定肩部。此外，将负功率降至最低所需的肌肉条件也被认为很重要。进行此类分析需要一个逆动力学模型。为了利用肩部机制的逆动力学模型，需要上肢骨骼的轨迹。由于目前尚无肩胛骨运动的动态非侵入性测量技术，本研究的目的是借助触诊技术记录肩胛骨在静态情况下的三维位置。在一台固定的轮椅测力计上，同时记录躯干、肩胛带和上肢的位置、十块肌肉的表面肌电图以及轮辋上的力。四名健康男性受试者参与了实验。测量了每个受试者在轮辋上的五个手部位置以及每个手部位置的五种不同负荷水平。使用先前开发的肩部机制肌肉骨骼模型（Van der Helm，1994a，《生物力学杂志》27(5) 551 - 569）进行逆静态模拟，计算肌肉力量。除了三块肌肉外，实测肌电图与计算得到的肌肉力量吻合良好。讨论了肩部机制各关节轴周围外部力与肌肉之间的力矩平衡。实验结果表明，需要大量肌肉活动来实现关节稳定。肩胛骨运动的实验结果将与动态条件下收集的实验数据相结合，用于该模型在动态情况下的应用。研究得出结论，肩部机制的肌肉骨骼模型在确定肌肉贡献和形态结构上的机械负荷的研究中非常有用。
