Isolated muscle-tendon units reject a broad range of perturbations without feedback

Animals easily navigate complex terrain and can rapidly and safely reject unexpected perturbations. However, the underlying mechanism at the muscle-tendon level of this behaviour is unclear. To study this, we attached a real muscle-tendon unit to a novel bio-robotic interface that emulates interaction with a mass in gravity to generate stable feedforward hopping. We then suddenly drop the height of the ground. We show that real muscle-tendon units can rapidly and safely reject perturbations within two hops across a large range of drop heights. This shows muscle-tendon units are robust against perturbations that span an order of magnitude in drop height during cyclic tasks without relying on closed loop feedback.