Effects of the walk ratio on the effectiveness of mechanical energy utilization during gait in healthy young people

When walking freely, humans prefer maintaining a nearly constant walk ratio (WR) (step length/cadence). An unnatural WR requires greater metabolic energy expenditure, with mechanical power demands underlying the metabolic response. To investigate the effects of WR on the effectiveness of mechanical energy utilization during walking, this study compared the average total absolute mechanical power during the stance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mstyle> <mml:mrow> <mml:msub><mml:mover><mml:mi>P</mml:mi> <mml:mo>-</mml:mo></mml:mover> <mml:mtext>total, stance</mml:mtext></mml:msub> </mml:mrow> </mml:mstyle> </mml:math> ) and swing ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mstyle> <mml:mrow> <mml:msub><mml:mover><mml:mi>P</mml:mi> <mml:mo>-</mml:mo></mml:mover> <mml:mtext>total, swing</mml:mtext></mml:msub> </mml:mrow> </mml:mstyle> </mml:math> ) phases between preferred and unnatural WRs at a fixed walking speed. Twenty healthy participants walked at their preferred WR and at six types of unnatural WRs at a preferred walking speed. The unnatural WRs comprised six cadence conditions (±10, ±15 and ±20 of preferred cadence). <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mstyle> <mml:mrow> <mml:msub><mml:mover><mml:mi>P</mml:mi> <mml:mo>-</mml:mo></mml:mover> <mml:mtext>total, stance</mml:mtext></mml:msub> </mml:mrow> </mml:mstyle> </mml:math> was significantly higher at high WRs (slower cadence) than at the preferred WR (<i>p</i> < 0.05) owing to an increased braking ground reaction force and shorter relative stance phase duration. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mstyle> <mml:mrow> <mml:msub><mml:mover><mml:mi>P</mml:mi> <mml:mo>-</mml:mo></mml:mover> <mml:mtext>total, swing</mml:mtext></mml:msub> </mml:mrow> </mml:mstyle> </mml:math> was significantly higher at low WRs (faster cadence) than at the preferred WR (<i>p</i> < 0.05) owing to the hip and knee joint powers being applied strongly and synchronously to prevent excessive knee flexion and extension. The preferred WR can optimize the effectiveness of mechanical work production, which may help to minimize metabolic energy expenditure.