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.