Meeting Abstract
Skeletal muscles generate the mechanical work needed to accelerate or raise an animal’s center of mass during locomotion. Therefore, a muscle’s capacity to generate mechanical work can be an important determinant of locomotor performance. The work generated by muscle is the product of active force produced by contractile tissues and the shortening undergone. During shortening, the muscle must bulge outwards to remain isovolumetric. This bulging may be restricted by the network of connective tissues that surrounds muscles. Hence, connective tissue constraints to shortening may impact a muscle’s ability to generate work. We modeled the interaction between muscle and connective tissue using a pressurized, fiber-wound cylinder to define the conditions where connective tissues may limit muscle work. This model was combined with two sets of experiments. In the first we compared the shortening and mechanical work capacity of a muscle with and without the presence of a physical constraint that restricted radial expansion. In the second we compared the shortening and mechanical work capacity of fiber bundles from a fibrotic (old) muscle before and after the application of a collagenase treatment. In these experiments, the collagenase decreased the connective tissue structure within the muscle and likely released the physical constraints to radial expansion. Taken together, our results show that shortening and mechanical work are constrained when the radial expansion of a muscle is restricted and that removing such constraints can recover the capacity to generate work. This work elucidates how the fundamental interactions between contractile and connective tissue structures affect contractile performance.
