Gait initiation, the transition from upright stance to steady state gait, requires the asymmetrical use of the two lower limbs. The initial stepping limb, called the lead leg, is mainly used to generate forward thrust, while the non-stepping, trailing limb is initially responsible for the generation of forward propulsion and the maintenance of body stability. For individuals with a unilateral below-knee amputation (BKA), this unequal sharing of responsibilities poses a potential conflict, as the prosthetic limb is known to have limitations in both stability and propulsion. Because the magnitude of this effect may differ depending upon the roles of each limb, the study hypothesized that individuals with a unilateral below-knee amputation would undergo unique postural and movement adaptations depending on the choice of the leading limb.

Eleven individuals with a unilateral BK A and eleven control subjects were recruited for this study. From a standing position, each individual initiated gait at three step length conditions (+0%, +25%, and +50% of preferred step length). Half of the trials were initiated with the right limb, while the other half were initiated with the left.

It was found that the amputees underwent postural and movement adaptations due to the presence of the prosthetic limb. The amputees required more time to initiate gait, applied a smaller magnitude of peak propulsive force, and exhibited a smaller displacement of the center of pressure. The magnitude of these changes was, however, found to be dependent upon the choice of the leading limb, as greater compensations were observed during the prosthetic trail limb condition.

Three conclusions were made from this study. First, the prolonged task duration allowed the amputees to apply a larger horizontal impulse, such that they were able to fully compensate for the decreased propulsive ability of the prosthetic limb. Second, the slower rate of initiation and the decrease in displacement of the center of pressure allowed the amputees to remain more stable throughout the entire task. Finally, it appeared that the role of the trailing limb had a greater impact during gait initiation and thus, leading with the prosthetic limb resulted in fewer postural and movement adaptations.