Meeting Abstract
During contraction, muscles must do internal work to deform their tissue and in particular to overcome the inertia of the individual elements within the muscle. However, the contribution of the internal mass within a muscle to the mechanical output of that muscle has only rarely been studied. As muscle size increases the inertial load will increase in proportion to the muscle mass, yet the force available to accelerate that mass will increase with the cross-sectional area of the muscle or muscle fibres. Thus, there should be a scaling effect of this inertial cost to contraction with a higher specific cost when progressing from single fibres to whole muscles, and similarly from small muscle to large muscle. A similar effect should be seen across different activation levels because the force available within the muscle increases with activity, even though the inertial load would remain the same. Here we use a dynamic, multi-element Hill-type muscle model to understand the effects of the inertial mass within the muscle on its contractile performance. The results show that the maximum strain-rate of a muscle (negative during contraction) is slower for large muscles but increases at higher activation. The curvature of the force-velocity relation increases for large muscles but decreases at high activations, even when the fibre-type of the muscle is held constant. Faster fibre-types appeared more sensitive to size and activation than did the slower muscles. This study highlights how estimates of the intrinsic speed of muscle fibres will be under-estimated when measured from whole muscles, and how the contractile performance of muscles from larger species may be reduced even when they contain the same fibre-types as muscle from smaller species.
