Because the force produced by muscle fibers declines in a hyperbolic fashion as shortening velocity increases, there is an optimal shortening velocity for power production. Consequently, performance in acceleration would be maximized if muscles were to shorten continuously at their optimal velocity. This could happen if the gear ratio of a muscle increased as the joint extended. We have begun to address whether or not this type of dynamic gearing actually happens in running and jumping mammals.
OUR STUDIES
Carrier, D. R., N. C. Heglund and K. E. Earls. (1994). Variable gearing during locomotion in the human musculoskeletal system. Science 265, 651-653. Full text of this article in PDF
Carrier, C. R., C. S. Gregersen and N. A. Silverton. (1998). Dynamic gearing in running dogs. J. Exp. Biol. 201, 3185-3195. Full text of this article in PDF
Gregersen, C. S., N. A. Silverton, and D. R. Carrier. (1998). External work and potential for elastic storage of energy at the limb joints of running dogs. J. Exp. Biol. 201, 3197-3210. Full text of this article in PDF
Gregersen, C. S. and D. R. Carrier. (2004). Dynamic gearing during jumping in dogs. J. Biomech. 37, 1011-1018. Full text of this article in PDF
SELECTED STUDIES RELATED TO THIS TOPIC BY OTHER AUTHORS
Roberts, T. J. and Marsh, R. L. (2003). Probing the limits to muscle-powered accelerations: lessons from jumping bullfrogs. Journal of Experimental Biology 206, 2567-2580.
Brainerd, E. L. and Azizi, E. (2005). Muscle fiber angle, segment bulging and architectural gear ratio in segmented musculature. Journal of Experimental Biology 208, 3249-3261.
Karamanidis, K. and Arampatzis, A. (2007). Aging and running experience affects the gearing in the musculoskeletal system of the lower extremities while walking. Gait and posture 25, 590-596.
Azizi, E. and Brainerd, E. L. (2007). Architectural gear ratio and muscle fiber strain homogeneity in segmented musculature. Journal of Experimental Zoology Part A: Ecological Genetics and Physiology 307, 145-155.
Azizi, E., Brainerd, E. L. and Roberts, T. J. (2008). Variable gearing in pennate muscles. Proceedings of the National Academy of Sciences 105, 1745-1750.
Braunstein, B., Arampatzis, A., Eysel, P. and Brüggemann, G. P. (2010). Footwear affects the gearing at the ankle and knee joints during running. Journal of biomechanics 43, 2120-2125.
Azizi, E. and Roberts, T. J. (2013). Variable gearing in a biologically inspired pneumatic actuator array. Bioinspiration & biomimetics 8, 026002.