WalkEnergy · Understanding the energetic cost of walking through computer simulations based on biophysical muscle models.

Metabolic energy consumption during walking increases considerably with disease, injury and age. We poorly understand why, because experimental estimates of energetic cost are limited to average whole-body measures. This lack of knowledge hinders the design of interventions that target walking energetics. Model-based computer simulations have the potential to predict energetics of individual muscles over time, and can be used to elucidate causal relationships between musculoskeletal properties and walking energetics. But current simulations vastly underestimate changes in energetic cost across walking conditions. I hypothesize that errors in predicting the energetic cost of walking are due to using Hill-type models and energetics models, which employ phenomenological relations derived from controlled experiments that do not capture muscle operating conditions during walking. In contrast, biophysical muscle models capture the mechanisms underlying muscle mechanics and energetics, but have not been used in simulations of walking. This project aims to gain fundamental insight into walking energetics through incorporating biophysical muscle models into simulations of walking, revealing contributions of individual muscles and gait phases to overall energetic cost, and predicting the energy savings enabled by assistive devices. This approach is feasible given my expertise with biophysical models and the host’s advancements in simulations, enabling the use of more complex muscle models. I will first develop a biophysical model that – when integrated in musculoskeletal simulations – captures whole-body energetics. I will then use the developed simulations to study muscle energetics across a range of walking conditions, and test the ability of the framework to predict exoskeleton assistance that maximizes energy savings. The developed (open-source) simulations may serve as a go-to tool to design interventions to improve mobility of individuals with increased energetic cost.