The effect of intrinsic muscular nonlinearities on the energetics 1 of locomotion in a computational model of an anguilliform

8 Animals move through their environments using muscles to produce force. When an animal’s nervous 9 system activates a muscle, the muscle produces different amounts of force depending on its length, its 10 shortening velocity, and its time history of force production. These muscle forces interact with forces from 11 passive tissue properties and forces from the external environment. Using an integrative computational 12 model that couples an elastic, actuated model of an anguilliform, lamprey-like swimmer with a surround13 ing Navier-Stokes fluid, we study the effects of this coupling between the muscle force and the body 14 motion. Swimmers with different forms of this coupling can achieve similar motions, but use different 15 amounts of energy. The velocity dependence is the most important property of the ones we considered for 16 reducing energy costs and helping to stabilize oscillations. These effects are strongly influenced by how 17 rapidly the muscle deactivates; if force decays too slowly, muscles on opposite sides of the body end up 18 fighting each other, increasing energy cost. Work-dependent deactivation, an effect that causes a muscle 19 to deactivate more rapidly if it has recently produced mechanical work, works together with the velocity 20 dependence to reduce the energy cost of swimming. 21