Fig. 1. A diagram of the model for muscle-powered accelerations at rest (A) and during a contraction (B). To simulate a muscle–lever–load system (inset) with an effective mechanical advantage that could vary during the contraction, the muscle–tendon unit operated across a gearing system that included a controllable gearbox to accelerate a load. The muscle consisted of several actuators acting in parallel to produce muscle force–velocity, length–tension and activation properties. The movement was subject to inertial and gravitational forces. The properties and dimensions of the muscle and the load were chosen to approximate the entire hindlimb and body of a jumping frog.