Investigating centre of mass stabilisation as the goal of posture and movement coordination during human whole body reaching

In the light of experimental results showing significant forward centre of mass (CoM) displacements within the base of support, this study investigate d if whole body reaching movements can be executed whilst keeping the CoM f ixed in the horizontal axis. Using kinematic simulation techniques, angular configurations were recreated from experimental data imposing two constrai nts: a constant horizontal position of the CoM and an identical trajectory of the hand to grasp an object. The comparison between recorded and simulat ed trials showed that stabilisation of the CoM was associated with greater backward hip displacements, which became more marked with increasing object distance. This was in contrast to recorded trials showing reductions in ba ckward hip displacements with increasing distance. Results also showed that modifications to angular displacements were necessary only at the shoulder and hip joints, but that these modifications were within the limits of joi nt mobility. The analysis of individual joint torques revealed that the pat tern and timing of simulated trials were similar to those recorded experime ntally. Peak joint torque values showed particularly that keeping the CoM a t a constant horizontal position resulted in significantly smaller ankle pe ak flexor and extensor torques. It may be concluded from this study that 's tabilising' the CoM during human whole body reaching represents a feasible strategy, but not the one chosen by subjects under experimental conditions. Our results also do not support the idea of the CoM as the stabilised refe rence value for the coordination between posture and goal-directed movement s.