Muscle function changes to meet the varying mechanical demands of locomotion across different gait and grade conditions. A muscle's work output is determined by time-varying patterns of neuromuscular activation, muscle force and muscle length change, but how these patterns change under different conditions in small animals is not well-defined. Here we report the first integrated in vivo force-length and activation patterns in rats, a commonly used small animal model, to evaluate the dynamics of two distal hindlimb…