Abstract
During human walking, the centre of mass (COM) laterally oscillates, regularly transitioning its position above the two alternating support limbs. To maintain upright forward-directed walking, lateral COM excursion should remain within the base of support, on average. As necessary, humans can modify COM motion through various methods, including foot placement. How the nervous system controls these oscillations and the costs associated with control are not fully understood. To examine how lateral COM motions are controlled, healthy participants walked in a ‘Movement Amplification’ force field that increased lateral COM momentum in a manner dependent on the participant's own motion (forces were applied to the pelvis proportional to and in the same direction as lateral COM velocity). We hypothesized that metabolic cost to control lateral COM motion would increase with the gain of the field. In the Movement Amplification field, participants were significantly less stable than during baseline walking. Stability significantly decreased as the field gain increased. Participants also modified gait patterns, including increasing step width, which increased the metabolic cost of transport as the field gain increased. These results support previous research suggesting that humans modulate foot placement to control lateral COM motion, incurring a metabolic cost.
Highlights
During normal human forward walking, the body’s centre of mass (COM) smoothly oscillates from side to side
Increasing step width may be beneficial for controlling lateral COM motion and increasing gait stability—the ability to reject or recover from small external perturbations and return to a steady state [13,14,15,16,17]
Net work was significantly ( p < 0.05) positive for the Amplification Low (0.0127 ± 0.0104 J/(stride × kg)) and Amplification High (0.0244 ± 0.0167 J/(stride × kg)) fields, confirming that forces were applied in the direction of COM velocity
Summary
During normal human forward walking, the body’s centre of mass (COM) smoothly oscillates from side to side. To avoid falls during walking, COM position needs to be maintained, on average, within the base of support, defined by the centre of pressure of the feet on the ground [4,5,6,7]. If not controlled, this laterally directed COM motion may pose a threat to upright walking. During normal walking people select step widths that minimize metabolic energy costs [2], but in the presence of external perturbations that challenge stability, people often select wider and more energetically costly steps [18,19,20,21,22,23]
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