Fig. 3

Continuous Relative Phase (CRP) Plots. Solid line indicates the sample mean and the shaded areas are the sample standard deviation. CRP at 0 indicates in-phase or both segments rotating together at the same rate in the same direction. ± 180 indicates anti-phase (segments rotating in opposite directions simultaneously at the same rate) between both segments; if the value is positive then the proximal segment is leading the distal segment; if the value is negative then the distal segment is leading the proximal segment. Shank-Foot and Thigh-Shank couplings demonstrated similar behaviors between limbs. However, the surgical limb Thigh-Shank coupling exhibited greater variability across subjects verified by different dynamic peak ranges of the knee. Additionally, the surgical limb shank-foot coupling was predominantly in phase for the entirety of swing phase (~ 57–100%) which is likely due to the passive feature of the prosthetic ankle joint. By contrast, for the Pelvis–Thigh coupling, the intact limb was more pelvis led while the surgical limb was more thigh led. Both limbs had greater variability across subjects compared to the other two couplings suggesting the Pelvis–Thigh coupling as the modulator for optimizing gait to compensate for the surgical knee (rotated ankle).