Fig. 1

Schematic illustration of the acting ankle moments and ankle motion on a slope. A Acting internal moments at the ankle due to the foot´s deflection, B sagittal angles on the slope, C ankle angle (yellow) and the maximum dorsiflexion angle (green) for the MPF-M and D schematic illustration of the MPF-M ankle motion for one gait cycle. A If the shank is rotated to an upright position from its neutral point (torque free position—dashed red line), the carbon heel spring is deflected and creates, due its internal moment M, a dorsiflexion moment for Down or a plantarflexion moment for Up, respectively. During Down, it pulls the knee into flexion and, during Up, it counteracts the forward rotation of the shank. Note that the reported external ankle moments act inversely to the internal ones. B Studied kinematic parameters were estimated for the sagittal plane—ankle angle (angle between toe, ankle and knee markers), knee angle (angle between ankle, knee, and trochanter markers) and shank angle (angle between ankle-knee marker line and vertical axis). (C) The MPF-M’s maximum dorsiflexion angle (green) is constant relative to the shank angle for level and UP. The ankle angle, in contrast, varies for the same shank angle