Mechanics and energetics of step-to-step transitions

The major determinant of walking’s metabolic cost is the work required to redirect the centre of mass velocity during step-to-step transitions. My first aim was to isolate transitions from other contributors to walking mechanics. The results demonstrated that sagittal plane rocking reproduced the important characteristics of walking’s transitions including a strong dependence of work on step length and a proportional increase in metabolic cost. My second aim was to use rocking to gain insight into pathological gait’s elevated cost. Physics-based mathematical models predict sub-optimal transitions occur when one or both legs are unable to generate mechanical power with the optimal timing and magnitude, requiring a greater magnitude of total work and an increase in metabolic cost. I tested this prediction by immobilising the ankle joints of healthy subjects to simulate sub-optimal transitions and found that joint immobilization indeed caused sub-optimal transitions thereby increasing transition work and metabolic cost.