Electromyographic Analysis of the Function of the Muscles Acting on the Ankle during Weight-Bearing with Special Reference to the Triceps Surae

¹ Detroit Orthopaedic Clinic, Detroit

Multilead electromyographic studies were made on ten normal young adults to investigate the function of the muscles acting on the ankle during weight-bearing activities. Action potentials were picked up with surface electrodes from the tibialis anterior, extensor digitorum longus, tibialis posterior, peroneus longus and brevis, medial and lateral gastrocnemius, soleus, and flexor digitorum longus. The activities performed were: relaxed standing, standing on an inclined and on a declined plane, shifting the body weight from the fore part of the foot to the heel, standing on one extremity, standing on the toes of both feet and on the fore part of one foot, relaxed walking, and stair-climbing. The evidence presented supports the following conclusions:

In the erect posture the gastrocnemius acts on the knee to maintain a slight degree of flexion. The medial head is more active than the lateral.

The soleus, in conjunction with the tibialis posterior and peroneus brevis, adjusts the position of the tibia on the tarsus and secondarily contributes to the femorotibial relationship at the knee.

At the ankle the act of standing up is controlled primarily by strong contraction of the tibialis anterior and extensor digitorum longus. These muscles stabilize the tibia on the tarsus as a person rises to an erect posture.

The magnitude of the action potentials of the leg muscles is the same, whether the subject stands on a level surface or on a plane inclined or declined to 20 degrees. The postural alignment of the body is automatically adjusted to keep its center of gravity over the center of the supporting base.

In the gait pattern, the gastrocnemius and soleus muscles stabilize the knee and ankle during the stance phase while the non-weight-bearing extremity is in the swing phase.

Additional studies of the action of the intrinsic and extrinsic muscles of the foot with particular reference to their specific roles in weight-bearing activities are needed. These studies would provide the basic understanding needed to plan the most effective treatment and reconstruction procedure to be used when normal function has been impaired.

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