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Abstract #0550

Dependence of the Ratio of Fiber Length Strain to Aponeurosis Strain (Gear Ratio) of the Human Medical Gastrocnemius on Anatomical Position and Loading Conditions

David Dongsuk Shin1, John A. Hodgson2, Gajanan Nagarsekar3, V Reggie Edgerton2, Shantanu Sinha3

1Biomedical Engieering, University of California, Los Angeles, CA, USA; 2Physiological Science, University of California, Los Angeles, CA, USA; 3Radiology, University of California, San Diego, CA, USA

Velocity encoded phase contrast MRI and a computer-controlled hydraulic ankle rotation apparatus were used to measure the in vivo gear ratio of the medial gastrocnemius (MG) in 6 healthy human subjects. The gear ratio changed significantly in three regions of MG, increasing from distal to proximal (distal: 1.00 0.03, mid: 1.10 0.02, proximal: 1.22 0.03). Slightly less gain was observed in passive (1.13 0.02) compared to active mode (1.08 0.03). For the first time, the architectural parameter of gear ratio and its variation with anatomical position under different loading and movement conditions were measured.