Stiffness of the gastrocnemius muscle and ankle joint under a cooling condition

Abstract

This study estimated the stiffness of the medial gastrocnemius muscle and ankle joint with decreased somatosensory input from the soles due to cooling. Two healthy young male volunteers participated in the experiment. The participants’ soles and the surface of the force plate were iced. Each participant stood quietly on the force plate. Electrical stimulation was applied to the medial gastrocnemius muscle. The center of pressure (COP) was measured with the force plate. The fluctuation of the COP due to electrical stimulation was extracted using a Kalman filter. The transfer function from the stimulation to the fluctuation was calculated using a system identification method. The poles of the transfer function were used to estimate the muscle and joint stiffness. The muscle and joint stiffness was decreased by cooling the soles.