Usually the strongest single axis in the machine — on both Unitree's H1-2 and G1 the knee peak exceeds the hip. Size it on peak rather than rated, because squatting, jumping and landing set the number, not steady walking; a common starting rule is a peak of two to four times the rated figure. Reduction has to stay low enough to remain backdrivable — a knee that cannot be driven backwards cannot absorb a landing or run a fall-protection routine.