Motor control enhancements by sub-threshold mechanical noise applied to foot soles during quiet standing

Intervention to improve the balance ability of individuals with impaired balance is needed to prevent falls. While sub-threshold mechanical noise applied to foot soles has been shown to improve balance not only for balance-impaired but also healthy individuals, how calf muscle activity is changed to enhance motor control to achieve improvement has not been explored. To address this issue, we study the calf muscle activity of healthy young adults standing on firm and compliant surfaces, with and without noise applied to their feet. The compliant surface experiment simulates balance impairment. Center of pressure (COP) data was used to assess balance changes, surface electromyography (EMG) recorded muscle activity, and COP-EMG correlations measured muscle contribution to postural control. The Wilcoxon signed-rank test was used to compare the data between the control and noise conditions. On both surfaces, the applied noise enhanced motor control efficiency of all three calf muscle groups studied - the tibialis anterior (TA), lateral gastrocnemius lateralis (LG), and medial gastrocnemius (MG). Noise also increased the contribution of the LG muscle group to postural control in the anteroposterior direction. Our finding suggests that, for balance-impaired individuals with weak calf muscles, higher-frequency noise should be used - this will increase motor control efficiency, i.e., increase posture correction frequency with concomitant reduction in calf muscle contractions, which is well-suited to the weak muscles.