Effects of Physiological Loading on the Achilles Tendon Moment Arm

Undergraduate: Ashish Khanchandani

Faculty Advisor: Jason Franz
Department: Biology

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The Achilles Tendon (AT) is a part of a human¿¿¿s musculoskeletal system that plays a role in the movement of the ankle and thus serves a function in locomotion. One measure of the effectiveness of the AT in force output is the AT moment arm. The AT moment arm is the distance from the line of action of the AT force and the center of rotation of the ankle joint. During the push-off phase of walking, the AT moment arm increases, although the mechanisms responsible for this change are poorly understood. Previous studies have only used isolated ankle exercises to quantify the AT moment arm, which may not represent dynamic movements. However, there is evidence suggesting that the AT moment arm exhibits complex behavior that is dependent both on ankle joint kinematics and dynamic muscle loading during movement. In addition, evidence suggests that the AT moment arm also varies between older and younger individuals. During these sets of experiments, we sought to investigate the mechanisms underlying this complex behavior by coupling quantitative motion analysis and dynamic ultrasound imaging of the AT and calf muscles. We hypothesize that the AT moment arm varies significantly due to muscle loading, governed by bulging during force generation, which is compromised by musculoskeletal changes due to aging effects. In order to investigate what causes AT moment arm to vary during isolated ankle exercises, three specific measurements were made using a Biodex machine.