Meeting Abstract
Organisms often are required to locomote in a changing environment while remaining stable. In order to do so, they must be able to quickly respond to a perturbation during locomotion. Muscles and other elastic elements in the body can respond to perturbations even before the nervous system can sense them. Moreover, the muscles change length and receive an activation signal, which means they may respond differently to the same perturbation at different times. My study investigates how muscle responds to short perturbations in length during a standard work loop protocol with different activation and perturbation phases. Isolated muscle samples from silver lamprey (Ichthyomyzon unicuspis) were sinusoidally shortened and lengthened at 1Hz and then stimulated at four phases. The muscle segment was then given lengthening perturbations at four different phases. The resulting muscle force and length were recorded. Maximum force, stiffness, and damping were quantified and compared between the activation and perturbation phases using ANOVA. When the muscle was perturbed at its maximum length, the maximum force was significantly higher than those of other perturbation phases. Similarly, muscle stiffness, as indicated by the slope of the force response during perturbation, was found to be greatest if the muscle was perturbed at the maximum length. This response may be reflective of the muscle’s intrinsic length-tension properties where muscles acting closer to plateau produce more force. At other perturbation phases, the muscle damping was much higher. The time course of the response to perturbations also differed depending on both perturbation and activation phase. In conclusion, both the phase of activation and perturbation affect how muscles respond to destabilizing length change.
