A variety of experimental and theoretical studies of muscle biophysics and the mechanics of locomotion are conducted in the Biomechanics Laboratory by Professor McMahon and his students and staff. Using analytical methods, including computer simulations based on differential-equation models of muscle function, they predict and measure how muscles behave mechanically during locomotion. For example, they have shown experimentally that to lengthen active muscle at high speeds requires more force than the muscle can bear at constant length. Comparison of this result with predictions of a mathematical model for cross-bridge dynamics leads them to conclude that the protein cross-bridge structures responsible for the force can sustain at least fivefold increases in length before the cross-bridge bond is forcibly ruptured.
Another project is concerned with the production of sounds by skeletal muscle. Muscles maintained in steady contraction make a low, rumbling sound audible with an ordinary acoustic stethoscope. Professor McMahonÕs group has shown that muscles in isolation from the body produce a ringing sound when given a single electrical stimulation. By measuring the pressure field around the muscle as it produces sound, they have tested various hypotheses concerning the soundÕs origin. Their measurements indicate that muscle stiffness rises well before tension develops in an isometric contraction. The measurement and interpretations of muscle sounds have applications in basic muscle biophysics and medicine.
The Laboratory maintains an interest in the physics of terrestrial locomotion by animals and legged robots. One current project, typical of several, uses computer simulations and experiments in which dogs, horses and legged robots run on treadmills to explore the competing effects of leg stiffness and gravity on running performance. In another project, the mechanism mechanism by which animals run on water is being studied.
Selected Publications:
Glasheen, J.W. and T.A. McMahon (1996). A hydrodynamic model of locomotion in the Basilisk Lizard. Nature 380:340-342.
Glasheen, J.W. and T.A. McMahon (1996). Size dependence of water-running ability in Basilisk Lizards. J. Exp. Biol. 199:2611-2618.
Glasheen, J.W. and T.A. McMahon (1996). Vertical water entry of disks at low Froude numbers. Phys. Fluids 8:2078-2083.