Meeting Abstract
Most of what we know about whole muscle contractile behaviour comes from measures on isolated muscle fibres or small muscles that have been extrapolated to larger sizes without considering the mechanical consequences of the additional muscle mass. Previous studies have shown that the mass of muscle tissue acts to slow the rate of force development and maximum velocity of muscle during shortening contractions and decrease the work and power per cycle during cyclic contractions. However, these studies have relied solely on model predictions and so the effects of inertial resistance due to tissue mass have not yet been confirmed by experiments on living tissue. Therefore, in this study we conducted in situ work-loop experiments on rat plantaris muscle (n = 7) to determine the effects of increasing the internal mass of muscle on contractile performance. We also simulated the in situ experimental conditions using a mass-enhanced Hill-type muscle model to validate the results of the previous modelling studies. We found that experimentally increasing the mass of in situ muscle results in lower mechanical work per cycle, and this result was confirmed in the model simulations. Further, we found that this mass-dependent reduction in work is influenced by the muscle length change per contraction cycle, with greater length changes resulting in greater reductions in work. These results confirm that muscle mass is an important consideration for a complete understanding of whole muscle contractile behaviour.
