Effects of Increased Arm Muscle Tone on Postural Recovery from External Forces: A simulation study

Muscle tone contributes to the maintenance of standing posture against external forces, but the effects of changes in the magnitude of muscle tone in the arms are not fully clear. This study aimed to investigate the effects of increased muscle tone in the arms during postural recovery from external forces. Perturbed stance simulations, in which a neural controller controlled a musculoskeletal model under three different arm muscle tone conditions were performed. The lower body muscles were controlled by the sum of constant values that corresponded to muscle tone and feedback control components, based on muscle length and lengthening velocity. Additionally, the arm muscles were controlled by the sum of constant values and feedback control components based on head and angular acceleration. The control parameters were optimized to minimize center-of-mass movement. Consequently, the center-of-mass motion was maximized under conditions of high arm muscle tone. This suggests that an increased arm muscle tone is detrimental to the maintenance of standing balance.