Medial gastrocnemius muscle stiffness dependent on gait speed

The purpose of this study is to clarify the relationship between gastrocnemius muscle stiffness and gait speed. Eight males participated in this experiment and walked at 2, 3, 4, and 5 km/h on a treadmill. Electrical stimulation was percutaneously applied to the medial gastrocnemius muscle once every two push offs, 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 natural frequency was calculated from the transfer function. The natural frequency was used as an index of stiffness. Two natural frequencies increased as gait speed increased; however, one natural frequency did not. The increased natural frequencies might be related to the muscle contraction, and the unchanged frequency might be related to the skin and subcutaneous tissue. In conclusion, medial gastrocnemius muscle stiffness increased as gait speed increased.