Reducing human energy expenditure for naturally efficient locomotion using passive support

In this study a model was introduced which simulates the effects of passive walking support on the human body. Passive support was designed with the goal to reduce human energy expenditure for walking. The XPED exoskeleton and three alternative exoskeleton configurations were tested. The XPED is an exoskeleton with two artificial tendons, passive elastic structures which provide a moment at the hip, knee and ankle joint. In previous research, simulation showed 42.5% reduction in joint work. In experiments however, no reduction in energy expenditure was measured. The old simulation model lacks modelling of human anatomy. This was considered a very important reason for the mismatch which was seen between reduction in energy expenditure in the model and with experiments. The new model includes the modelling of human muscles, tendons, and dissipation of negative work. This also enabled new measures for energy expenditure: muscle work, in which eccentric muscle work contributes less than concentric muscle work, and muscle moments. It was hypothesised that with this new model the work efficiency, the amount of reduction in work, of the XPED exoskeleton would be predicted much lower. The new model showed 37.0% reduction in muscle work. Although efficiency was lower, the presence of anatomic structures in the model did not greatly affect the functionality of the XPED. An optimisation of the XPED parameters to the new work measure for energy expenditure even brought work efficiency up to 43.6%. The other support configurations provided support at the hip, at the knee, or at the hip and the knee joint. It was hypothesised that these configurations were as efficient as the XPED, since mechanical work at the ankle is already performed passively to large extent. This had to be rejected. Work efficiencies of the hip, knee and combined support were respectively 18.7%, 18.4% and 37.1%. Although efficiencies were lower, these configurations are still worth evaluating since they have the benefit that the exoskeleton can be smaller and that the naturally present and very efficient energy saving mechanism in the ankle is not disturbed. A pilot experiment where these configurations were tested with the LOPES exoskeleton did not prove reduction in energy expenditure.BMDBioMechanical EngineeringMechanical, Maritime and Materials Engineerin