Predicting the variance in movement energetics within individuals: integrating muscle energetics into musculoskeletal models

Glen Lichtwark

Queensland University of Technology, Australia

Whilst the fundamental mechanisms of muscle contraction energetics are relatively well characterised, linking this knowledge to predict the variance in whole animal energy consumption under different movement or locomotor conditions remains a challenge. The vast number of muscles involved, contributions of elastic tissue energy recycling, interaction with the external environment and how the nervous system adjusts control in response to different locomotor constraints add to the complexity of predicting movement energetics. Musculoskeletal models that can resolve muscle force requirements to produce a specific movement can be incorporated with phenomenological models representing energy output (work + heat), however such models are rarely validated across a range of conditions to examine their sensitivity. Across a number of studies on human locomotion (hopping, walking, cycling), we have explored the capacity of musculoskeletal models to predict the rate of energy consumption across a range of movement constraints (e.g. ground contact time, stride/hop frequency, cycling cadence and power output). Such studies reveal how the costs of generating (or absorbing) mechanical work can vary under different conditions due to contractile conditions induced by the locomotor requirements and the subsequent activation and/or shortening requirements. Further simplification of such models to represent abstract contractile requirements during spring-mass like motion demonstrate the importance of mechanical interaction with the environment and elastic energy storage and return and provides a framework to investigate the cost of locomotion across different individuals and/or species. Such models can have broad applicability in understanding how morphological and environmental conditions affect cost of locomotion.