MULTIJOINT COORDINATION STRATEGIES FOR STRAIGHTENING UP MOVEMENT IN HUMANS

Complex movement execution theoretically involves numerous biomechanic al degrees of freedom, leading to the concept of redundancy. The kinem atics and kinetics of rapid straightening up movement from the squatti ng position were analysed with the optoelectronic ELITE system in 14 s ubjects. We found multiple acceleration and deceleration peaks for the hip, knee and ankle joints during the early extension phase of the mo vement. In order to test the temporal coordination between the angular acceleration of these joints, conjugate crosscorrelation functions (C CF) between each set of two variables were calculated. We found a bimo dal distribution of the maximum CCF in positive and negative values su ggesting the existence of two distinct strategies, the in-phase and th e out-of-phase strategy for each pair of joints. The hip and knee coor dination strategies (in-or out-of-phase) were well conserved in each s ubject for repetitive movements. Combination of joint pair strategies was more reproducible for the hip-knee/knee-ankle pair than for the ot her combinations, suggesting that the straightening up strategies are organised around the knee. We conclude that mastering of the redundanc y problem can be realised by using coordination strategies characteris ed by opposed joint acceleration patterns. (C) 1998 Published by Elsev ier Science Ireland Ltd.