Stiffness estimation of the medial gastrocnemius muscle in toe walking

The purpose of this study is to estimate the stiffness of the medial gastrocnemius muscle in toe walking. Five young males participated in this experiment and walked at 3 km/h on a treadmill. Electrical stimulation was percutaneously applied to the medial gastrocnemius muscle at every second toe strike or terminal stance, and the mechanomyogram was measured. The evoked mechanomyogram was extracted by subtracting the walking vibration from the measured mechanomyogram. The evoked mechanomyogram system was identified using a singular value decomposition method, and the stiffness was calculated from the transfer function. The evoked mechanomyograms at both toe strike and terminal stance were approximated well with the third-order models. The stiffness in toe walking was larger than that in normal walking at both toe strike and terminal stance. The increase of the stiffness in toe walking might be caused by the muscle shape and muscle activity.