Optimal motions and actuator inputs for the rotary gear box with friction and frictionless case. Shown are the results for positive mechanical motor work (a), thermal losses (b), and electrical work (c). The most notable difference from the frictionless motion was that for PEA electrical work, it was no longer optimal to have the leg oscillate during flight. Instead, PEA and SEA adopted similar strategies during flight, holding their legs near maximum extension.