Compensatory mechanisms in below-knee amputee gait in response to increasing steady-state walking speeds

Compensatory mechanisms in below-knee amputee gait are necessary due to the functional loss of the ankle muscles, especially at higher walking speeds when the mechanical energetic demands of walking are greater. The objective of this study was to examine amputee anterior/posterior (A/P) ground reaction force (GRF) impulses and joint kinetics across a wide range of steady-state walking speeds to further understand the compensatory mechanisms used by below-knee amputees. We hypothesized that amputees would rely more on their intact leg to generate greater propulsion relative to the residual leg, which would result in greater GRF asymmetry between legs as walking speed increased. Amputee and control subject kinematic and kinetic data were collected during overground walking at four different speeds. Group (n = 14) average amputee data showed no significant differences in braking or propulsive GRF impulse ratios, except the propulsive ratio at 0.9 m/s, indicating that the subjects maintained their initial levels of GRF asymmetry when walking faster. Therefore, our hypothesis was not supported (i.e., walking faster does not increase GRF loading asymmetry). The primary compensatory mechanism was greater positive residual leg hip joint power and work in early stance, which led to increased propulsion from the residual leg as walking speed increased. In addition, amputees had reduced residual leg positive knee work in early stance, suggesting increased output from the biarticular hamstrings. Thus, increasing residual leg hip extensor strength and output may be a useful mechanism to reduce GRF loading asymmetry between the intact and residual legs.