Meeting Abstract
42.6 Jan. 6 Elastic properties of muscle during active shortening MONROY, J.A.*; GILMORE, L.A.; KREBS, L.; LAPPIN, A.K.; LINDSTEDT, S.L.; PIEROTTI, D.J.; NISHIKAWA, K.C.; Northern Arizona University Jenna.Monroy@nau.edu
Recent work demonstrates that muscles themselves store elastic energy during isometric tetanus. When the force is reduced rapidly, muscles recoil elastically. Elastic recoil of muscle contributes to high power output of ballistic movements. At maximum isometric force, the depressor mandibulae muscles of toads develop strains up to 17.5% ML. This study tested the hypothesis that elastic properties of toad depressor mandibulae muscles are particularly adapted for power enhancement compared to other skeletal muscles. Using load-clamp experiments, we quantified the elastic properties of a variety of vertebrate muscles, including the depressor mandibulae muscles of Ceratophrys (which lacks ballistic tongue projection), the soleus (slow) and extensor digitorum longus (fast) muscles of Mus, and the semimembranosus and sartorius muscles of Rana. From the load-clamp data, we calculated the displacement from equilibrium (x) and spring constant (km) of each muscle. Our results demonstrate that all muscles responded similarly to changes in load. For a given initial level of force, the displacement from equilibrium increased exponentially as the change in force increased. The spring constant decreased non-linearly with the change in force, providing self-stabilization. All muscles experienced displacements of ~ 8% ML when the load was reduced to ~ 10% maximum isometric force. Maximum observed shortening was 15.3�19.4%�ML at the lowest loads. These results suggest that the displacement from equilibrium of intrinsic elastic elements within muscle is constant, relative to muscle length, across different muscles and different species, and that the ability to recoil elastically during rapid unloading is a general feature of skeletal muscle.
