A SIMPLE-MODEL FOR FAST PLANAR ARM MOVEMENTS - OPTIMIZING MECHANICAL ACTIVATION AND MOMENT-ARMS OF UNIARTICULAR AND BIARTICULAR ARM MUSCLES

In this study a simple model of a two segmented arm with only two musc les is used to study an underarm throw and an overarm stroke. There is a uniarticular shoulder muscle and an elbow muscle with facultatively an additional moment arm on the shoulder. The effect of changing the shoulder moment of the latter muscle, and of changing its mechanical d elay is measured. The effect of tendons is assessed, and of throwing o r striking using heavy weights. Some of the trials are analysed in det ail to answer the question why some results are better than others. Wi th uniarticular muscles we always found a proximal-distal sequence in muscle activity, but with a biarticular muscle sometimes this sequence can be absent. Tendons and the weight that is held do influence the o ptimal delay, but not the optimal moment arm. The model predicts a dif ferent optimal technique for a stroke with a light or a heavy tool. (C ) 1997 Academic Press Limited.