Energy flow analysis of amputee walking shows a proximally-directed transfer of energy in intact limbs, compared to a distally-directed transfer in prosthetic limbs at push-off.

Reduced capacity and increased metabolic cost of walking occurs in amputees, despite advances in prosthetic componentry. Joint powers can quantify deficiencies in prosthetic gait, but do not reveal how energy is exchanged between limb segments. This study aimed to quantify these energy exchanges during amputee walking. Optical motion and forceplate data collected during walking at a self-selected speed for cohorts of 10 controls, 10 unilateral trans-tibial, 10 unilateral trans-femoral and 10 bilateral trans-femoral amputees were used to determine the energy exchanges between lower limb segments. At push-off, consistent thigh and shank segment powers were observed between amputee groups (1.12W/kg vs. 1.05W/kg for intact limbs and 0.97W/kg vs. 0.99W/kg for prosthetic limbs), and reduced prosthetic ankle power, particularly in trans-femoral amputees (3.12W/kg vs. 0.87W/kg). Proximally-directed energy exchange was observed in the intact limbs of amputees and controls, while prosthetic limbs displayed distally-directed energy exchanges at the knee and hip. This study used energy flow analysis to show a reversal in the direction in which energy is exchanged between prosthetic limb segments at push-off. This reversal was required to provide sufficient energy to propel the limb segments and is likely a direct result of the lack of push-off power at the prosthetic ankle, particularly in trans-femoral amputees, and leads to their increased metabolic cost of walking.

Medial-lateral centre of mass displacement and base of support are equally good predictors of metabolic cost in amputee walking.

Amputees are known to walk with greater metabolic cost than able-bodied individuals and establishing predictors of metabolic cost from kinematic measures, such as centre of mass (CoM) motion, during walking are important from a rehabilitative perspective, as they can provide quantifiable measures to target during gait rehabilitation in amputees. While it is known that vertical CoM motion poorly predicts metabolic cost, CoM motion in the medial-lateral (ML) and anterior-posterior directions have not been investigated in the context of gait efficiency in the amputee population. Therefore, the aims of this study were to investigate the relationship between CoM motion in all three directions of motion, base of support and walking speed, and the metabolic cost of walking in both able-bodied individuals and different levels of lower limb amputee. 37 individuals were recruited to form groups of controls, unilateral above- and below-knee, and bilateral above-knee amputees respectively. Full-body optical motion and oxygen consumption data were collected during walking at a self-selected speed. CoM position was taken as the mass-weighted average of all body segments and compared to each individual's net non-dimensional metabolic cost. Base of support and ML CoM displacement were the strongest correlates to metabolic cost and the positive correlations suggest increased ML CoM displacement or Base of support will reduce walking efficiency. Rehabilitation protocols which indirectly reduce these indicators, rather than vertical CoM displacement will likely show improvements in amputee walking efficiency.