Natural frequencies of brachii muscle at various contraction levels

The natural frequencies of the longitudinal and radial directions of the biceps brachii muscle were estimated by measuring evoked torque and muscle oscillation, respectively. The purpose of this study is to reveal the relation between the natural frequencies of longitudinal and radial directions to the biceps brachii muscle. An electrically stimulated evoked torque and mechanically stimulated evoked muscle oscillation were measured with a strain gauge load cell and myotonometer, respectively. The measurement was carried out during a resting state and an isometric contraction. The systems of the evoked torque and the muscle oscillation were identified. The natural frequency of the systems was calculated from the poles of the transfer function. In conclusion, the frequency of evoked torque and muscle oscillation increased as the muscle contraction level increased. It is suggested that the natural frequency of the axial direction might be estimated from the natural frequency of the radial direction of the muscle.