We currently have little understanding of how hydrodynamic perturbations affect the neuromuscular control of locomotion, in contrast to the extensive literature available for studies of steady swimming. Observations have shown that fishes in current-swept environments position themselves in the wake behind objects to take advantage of the reduced velocity and presumably reduce muscle activity. Yet, kinematics alone cannot conclusively reveal mechanisms of flow exploitation or
the extent of energy expenditure involved under these circumstances. When muscle recordings and flow visualization techniques are employed in the laboratory , it is clear that trout holding station behind a cylinder are not just seeking refuge in reduced flow or using a rostrocaudal sequence of muscle activity, but using the energy of the vortices. This is because although the body participates in a large-amplitude mechanical wave.