Independent motor unit recruitment reduces the predicted metabolic cost of locomotion

Muscle-based simulations have predicted the metabolic cost of locomotion with varying success. We investigated if independent recruitment of motor units within a muscle could reduce the predicted cost. We predicted metabolic cost using experimental data of walking and simulations that consisted of independently activated muscle fibres. Across objective functions and metabolic models, the simulations that allowed for independent muscle fibre recruitment predicted a lower metabolic cost compared with a mixed fibre model. Accounting for recruitment of fibre types in simulations improves physiological realism and reduces the predicted metabolic cost of locomotion.