Transtibial amputation increases the metabolic energy needed for stabilizing walking in the sagittal plane

Walking energy consumption is higher in people with versus without a transtibial amputation, but the underlying reasons are poorly understood. Active prostheses that restore ankle power fail to decrease walking energy consumption, suggesting that there should be other reasons than a lack of ankle power. Transtibial amputation impacts walking stability, as evidenced by the increased fall risk, and there is an energetic cost associated with stabilizing walking. It is, however, unclear how transtibial amputation affects the energetic cost of stabilizing walking. We assessed the metabolic cost of stabilizing walking against treadmill belt speed perturbations (SD=0.13 m/s) in 16 subjects with and 23 subjects without a transtibial amputation at three walking speeds between 0.6 and 1.6 m/s. We focused on sagittal plane stability, as a transtibial amputation mainly affects modulation of the ankle torque, and this ankle strategy contributes most to sagittal plane control of walking at low speeds. Perturbations induced 0.24 W/kg larger increases in energy consumption across walking speeds in subjects with than without a transtibial amputation. Whereas mean reductions in step length in response to perturbations were similar between groups, individuals with an amputation increased step length variability of their intact leg more - especially at low speeds - than individuals without an amputation. As continuous control is required for unperturbed walking, an increased metabolic cost of stabilizing walking might explain - at least partially - the higher energetic cost of walking. These insights are important when seeking to reduce the metabolic cost of walking after transtibial amputation. NEW & NOTEWORTHYThe higher metabolic cost of walking in individuals with versus without a transtibial amputation is poorly understood, hindering the design of interventions. We demonstrated that transtibial amputation considerably increases the energy consumption for stabilizing walking in the sagittal plane and increases the reliance on step length adjustments to stabilize walking. This opens up perspectives for restoring walking energetics after amputation through prostheses that support sagittal plane stability.