Meeting Abstract

42.4  Wednesday, Jan. 5  Complex interactions between length and force in the elastic behavior of active muscle. GILMORE, L.A.*; MONROY, J.A.; NISHIKAWA, K.C.; Northern Arizona University; Northern Arizona University; Northern Arizona University leslie.gilmore@nau.edu

Both the active force produced by a muscle and the passive force due to stretch depend on the length of the muscle. Therefore, we might expect that the elastic properties of actively shortening muscle would also exhibit a clear and predictable pattern of length dependence. Using a servo –motor force lever system to perform load clamp experiments, we examined the elastic behavior of mouse soleus muscles. In each load clamp experiment, a muscle is stimulated to maximal force prior to rapid unloading. We used this approach to characterize the shortening behavior exhibited during the fast phase of elastic recoil. In addition to characterizing each muscle at its optimal working length (Lo), we characterized the behavior of each muscle at lengths of 5, 15 or 25% greater than Lo. Length changes in this experiment were made prior to activation. Our results show that elastic behavior depends on changes in length, but is not predicted by the active, passive or total force as expected. Instead there is a more complicated relationship between the force production of the muscle and the length at which it is activated. Muscle stiffness during recoil is greatest at 115% of Lo but more compliant at Lo and 125% of Lo. This non-linear relationship suggests that an internal spring exists within the sarcomere which responds differently to stretch and activation. Supported by NSF IOS-1025806, IOS-0732949, II5-0827688, TRIF Fund for Biotechnology and Science Foundation Arizona.