Meeting Abstract

50.4  Sunday, Jan. 5 11:00  How does the velocity-dependent behavior of muscles change with activation? TAHIR, UH*; MONROY, JA; NISHIKAWA, KC; Northern Arizona University; Northern Arizona University; Northern Arizona University ut5@nau.edu

Despite the success of the sliding filament theory, many important properties of muscle remain unexplained. Surprisingly, the goal of predicting muscle force output during natural movements remains elusive, suggesting that the theory of muscle contraction is incomplete. Simple experiments using constant-velocity stretch and shortening of isolated muscles illustrate the non-linearity of muscle force output, which includes velocity- and history-dependent components. During constant velocity stretch, muscle force increases faster in the first 20 ms than during the next 50 ms of the stretch. There is a long-lasting increase in force (force enhancement) after stretch, and a long lasting decrease in force after shortening (force depression). In order to predict changes in muscle force during changes in length, we need to understand how the velocity-dependent behavior of muscle changes with activation. We investigated this using isovelocity stretch and shortening experiments in active and passive muscles. Soleus muscles from mouse was isolated and attached to a servomotor force lever. The muscles were then stretched or shortened through a range of initial lengths, velocities and activation levels. Activation of the muscle ranging from 0% to 100% was achieved by modulating the stimulation voltage and frequency. Preliminary results suggest that damping coefficients and the force-velocity relationship scale linearly from 0 – 100% activation. The results from these experiments have the potential to inform our understanding of muscle contraction and motor control, and to provide algorithms for controlling powered devices that, like muscles, will adapt instantaneously to changes in load. Supported by NSF IOS-1025806, IIP-1237878, and NSF BIOTEC 0742483.