Seeking for a better Human-Prosthesis energetic gait efficiency by quantifying both propulsion power and instability control

The present study aims at quantifying propulsion and dynamic balance through biomechanical parameters issued from theoretical modeling and analysis of locomotion during the gait of people using prosthetic devices. An experimental protocol combined motion capture and oxygen consumption quantification during gait on a treadmill. The mechanical work produced and dissipated by the lower limbs and the evolution of a biomechanical indicator of balance were used and the estimation of the metabolic cost of walking was made from oxygen consumption. To test the relevance of the chosen parameters, the experiments were performed on six able-bodied volunteers successively equipped with two prosthetic ankle-feet (elastic vs rigid) mounted on a femoral prosthetic simulator. For each participant, the parameters were computed and compared in three configurations: i/ without prosthesis, ii/ with rigid prosthetic ankle-foot iii/ with elastic prosthetic ankle-foot. The results put in evidence an increase of energy consumption in both prosthetic configurations compared to the configuration without prosthesis. However, no differences could be observed between the elastic and rigid prosthetic configurations. The analysis of mechanical work performed by each lower limb, which confirmed the energy delivered by the elastic foot during the propulsion, did not explain by its own this discrepancy. The maintenance of balance that seems to be more challenging during the double support in the elastic configuration could be involved in this counter-intuitive result. Finally, this preliminary study shows the importance to consider simultaneously propulsion and balance objectives during gait as they must both require muscular actions involved in the production of energy by the prosthesis user.