Analysis of the weight-transfer mechanism through forward velocity of the combined center of pressure during the loading response in individuals with unilateral transtibial amputation

Background: The dynamic stability during forward propulsion in the stance phase of prosthetic gait can be quantified using the center of pressure (COP). Although previous studies focused primarily on the single-limb support phase, COP movement during the double-limb support phase remains unclear. Objective: This study quantitatively analyzed the weight-transfer mechanism during gait by examining the forward velocity of the combined COP and the duration of the loading response (LR) on the prosthetic and intact sides. Method: This study conducted experiments involving 6 individuals with unilateral transtibial amputation and 11 able-bodied individuals. The participants were instructed to walk at 3 different speeds, and data were collected under each condition, using a 3D motion capture system. The peak value and timing of the forward velocity of combined COP in the LR were compared between the prosthetic and intact sides. Result: Regarding the forward velocity of the combined COP in the prosthetic-side LR, the peak value was smaller at slow walking speeds and the peak timing tended to be delayed under all walking-speed conditions compared with the intact-side LR. These parameters during the prosthetic-side LR were similar to those of able-bodied individuals. Analysis of the LR duration revealed no consistent trend in the relative durations of the prosthetic-side LR and intact-side LR. Conclusions: The results of this study suggest that individuals with unilateral transtibial amputation may employ a characteristic movement strategy during intact-side LR while the prosthetic side is in the pre-swing phase.