Ankle moment vs. relative angle curve for a representative subject walking at 1.75 m/s.

Letters a-f on the graph correspond to the poses schematically shown during a typical walking cycle (top, schematic timing is adapted from [69]). Quasi-stiffness is calculated based on the slope of the best-line fit to the moment-angle curve of b-c for the dorsi-flexion (), c-d for the dual-flexion (), and d-e for the plantar-flexion () phases of the progression period (b-e). The area enclosed by the graph represents the propulsion work of the ankle (). The joint excursion in each phase is the difference between the ankle relative angle at the onset and end of that phase (i.e. , and