Analysis of the function of Gastrocnemius and Soleus in ankle joint during jumping by means of physical model

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This research examined the role of bi- and mono-articular muscles related to the extension of ankle joint in jumping. The bi-articular muscle is the Gastrocnemius and the mono-articular muscle is the Soleus. A physical model that could be changed of the muscular arrangement was used in order to examine the functions of the Gastrocnemius and the soleus to the movement control.In a theoretical analysis, the functionally effective muscular strength concept about the two link system was applied to the shank, the functionally effective muscular strength concept about the shank was constructed, and the output distribution decision method at the toe was examined. As a result, when the Soleus and the Gastrocnemius were shortened, it became clear that the direction of the output force at the toe was changed from the vertical to horizontal and that there was a negative influence for jumping.Next, the change of muscle length and the muscle activity of the Gastrocnemius and the Soleus in jumping w … More ere examined. The motions of subjects in vertical jumping were videotaped by a digital video camera, and the change of muscle lengths of the Gastrocnemius and the Soleus were calculated. Moreover, the EMGs of muscles around the knee and ankle joint were derived.The following actuators were prepared as the actuator of the physical models for jumping. The springs were applied as the extension actuator of the knee and ankle joint, and the wire was applied as the bi-articular muscle Gastrocnemius. Four models were made by combining those actuator. The model (1)was equipped with only knee joint extension actuator. The model (2)was equipped with the knee joint extension actuator and the ankle joint extension actuator. The model (3)was equipped with the knee joint extension actuator and the bi-articular muscle Gastrocnemius. The model (4)was equipped with the knee extension actuator, the ankle extension actuator and the bi-articular muscle Gastrocnemius. The ankle joint of the model (1)was fastened because the ankle joint that was not equipped with actuator was not able to transmit power to the floor. As a result, the relation of the jumping heights of the models was that (3)>(4)>(2)≒(1). Moreover, the relation of the rotary frequency in the air was that (1)>(2)>(4)≒(3). These results indicate that the Gastrocnemius has the functions of increasing jumping height and stabilizing airborne posture, and that the soleus has not those functions. Less