Evaluating the energetics of entrainment in a human–machine coupled oscillator system

Abstract During locomotion, humans sometimes entrain (i.e. synchronize) their steps to external oscillations: e.g. swaying bridges, tandem walking, bouncy harnesses, vibrating treadmills, exoskeletons. Previous studies have discussed the role of nonlinear oscillators (e.g. central pattern generators) in facilitating entrainment. However, energetics such interactions are unknown. Given substantial evidence that prioritize economy during we tested whether reduced metabolic expenditure is associated with human entrainment vertical force oscillations, where frequency and amplitude were prescribed via a custom mechatronics system walking. Although cost was not significantly entrainment, individuals expended less energy when oscillation forces did net positive work on body roughly selected phase relationships maximize work. It possible use mechanical cues infer inform effective gait strategies. If so, an accurate prediction may rely relative stability environment. Our results suggest occurs over wide range parameters, though as direct priority for minimizing cost. Instead, act stabilize environment, thus increasing predictability implementation internal models guide minimization.