1 2 3 4 Inter - joint dynamic interaction 5 during constrained human quiet standing 6 examined by induced acceleration analysis 7 8

225 words] 33 34 Recent studies have demonstrated that human quiet standing is a multi-joint movement, 35 whereby the central nervous system (CNS) is required to deal with dynamic interactions 36 among the joints to achieve optimal motor performance. The purpose of this study was to 37 investigate how the CNS deals with such inter-joint interaction during quiet standing by 38 examining the relationship between the kinetics (torque) and kinematics (angular 39 acceleration) within the multi-degree-of-freedom system. We modeled quiet standing as a 40 double-link inverted pendulum involving both ankle and hip joints and conducted an 41 “induced acceleration analysis.” We found that the net ankle and hip torques induced 42 angular accelerations of comparable magnitudes to the ankle (3.8 ± 1.4 deg/s2 and 3.3 ± 1.2 43 deg/s2) and hip (9.1 ± 3.2 deg/s2 and 10.5 ± 3.5 deg/s2) joints, respectively. Angular 44 accelerations induced by the net ankle and hip torques were modulated in a temporally 45 anti-phase pattern to one another in each of the two joints. These quantitative and temporal 46 relationships allowed the angular accelerations induced by the two net torques to 47 counter-compensate one another, thereby substantially (~70%) reducing the resultant 48 angular accelerations of the individual joints. These results suggest that, by taking 49 advantage of the inter-joint interaction, the CNS prevents the net torques from producing 50 large amplitudes of the resultant angular accelerations when combined with the kinematic 51 effects of all other torques in the chain. 52