Meeting Abstract
During locomotion, animals often must cope with unexpected forces. These perturbations may cause an increase or decrease in length of their muscles. Although animals may sense these perturbations and change the way they are moving to compensate for them, the muscles themselves, separately from the nervous system, may help to compensate for perturbations. I investigated how brief shortening and lengthening perturbations at different phases affect muscle force during sinusoidal length changes. Muscle samples from silver lampreys (Ichthyomyzon unicuspis) were studied using a modified work loop protocol, in which small lengthening and shortening perturbations were added on top of an overall sinusoidal oscillation. While being lengthened and shortened at 1Hz, the muscle was activated electrically at four phases. We also applied lengthening or shortening perturbations at four phases. During each perturbation, we estimated the maximum force, stiffness and damping of the muscle. We compared these quantities between lengthening and shortening perturbations. We also compared how the muscle segment returns to its baseline oscillation after each perturbation. For both types of perturbations, if the perturbation is applied while the muscle is being lengthened, the forces are high . If the perturbations are applied during shortening, the forces are lower. Moreover, when the muscle segment is relatively short, the damping response is stronger than the elastic response. Overall, we find that muscle responds differently to lengthening and shortening perturbations, and the response depends on both activation and perturbation phase.
