Passive-dynamic ankle-foot orthoses change post-stroke lower extremity constituent work profile

Stiffness-customized passive-dynamic ankle-foot orthoses (PD-AFOs) have been shown to reduce the mechanical cost of transport (COT) of individuals post-stroke. However, the mechanisms underlying this reduced COT are unknown. Therefore, this study aimed to identify the factors driving COT reduction with PD-AFO use for individuals post-stroke. Results showed that changes in limb work were strongly correlated to changes in COT with the PD-AFO compared to No AFO in the paretic (tau = 0.637, p < 0.001) and non-paretic (tau = 0.621, p < 0.001) limbs. There was also a strong correlation between changes in limb work and changes in COT compared to SOC AFO in the paretic (tau = 0.569, p < 0.001) and non-paretic (tau = 0.503, p = 0.003) limbs. Conversely, changes in stride length and changes in COT were not correlated. Changes in COT between No AFO and PD-AFO were moderately correlated to the number of constituents that performed less mechanical work for both the paretic (tau = -0.462, p = 0.009) and non-paretic (tau = -0.402, p = 0.025) limbs. Compared to walking with SOC AFOs, there was a moderate correlation between COT and the number of constituents in the paretic limb (tau = -0.458, p = 0.011) but not the non-paretic limb (tau = -0.247, p = 0.173). These findings indicate that PD-AFOs reduce COT primarily through small changes in work across many lower limb constituents. Understanding how COT reduction occurs can help optimize PD-AFO design and possibly other rehabilitation interventions for individuals post-stroke.