Meeting Abstract

5.5  Thursday, Jan. 3  More boing for your buck: spring properties of muscle at and beyond optimal length. GILMORE, L.A.*; MONROY, J.A.; HOKANSON, J.; NISHIKAWA, K.C.; Northern Arizona University; Northern Arizona University; SUNY, Cortland; Northern Arizona University Leslie.Gilmore@nau.edu

A muscle produces maximal force when activated at its optimal length. If the muscle is rapidly unloaded at this length, it exhibits a fast recoil phase and then a slow phase of shortening. Distance and speed of recoil during the initial phase are determined by the elastic properties of the muscle, while the slow phase of shortening is a function of the cycling of the crossbridges with the thin filament. In this study, we investigated the effects of increases in muscle length on the fast recoil phase. We used a servo �motor force lever system to perform load clamp experiments on mouse soleus and EDL muscles. Prior to activation, muscle lengths were increased 5-25% beyond optimal lengths in order to measure the distance of shortening during the fast phase. Preliminary results show that, for a given change in load, as muscle length increases the distance shortened during the fast phase is greater. Remarkably, the stiffness decreases as the muscle length increases beyond the optimal length. These preliminary results appear to be consistent with the hypothesis that the viscoelastic titin protein contributes to both force enhancement with stretch and elastic recoil during rapid unloading in active muscle. Supported by NSF IOS-0623791, IOS-0732949, NIH R25-GM56931, the TRIF Fund for Biotechnology and Science Foundation Arizona.