Adaptation of functional gait parameters to a newly provided stiffness-optimized ankle-foot orthosis

Background: Clinical decisions regarding ankle-foot-orthosis stiffness in people with calf muscle weakness are based on immediate evaluations, not taking gait adaptation into account. This study examined adaptation of step length, walking speed and energy cost of walking in the 3-months post-provision and whether individuals with higher gait variability adapt more compared to individuals with lower gait variability. Methods: We conducted a post-hoc analysis in eighteen stiffness-optimized ankle-foot-orthosis users with bilateral calf muscle weakness. Gait biomechanics, step length, walking speed and walking energy cost directly after provision (T1) and 3-months post-provision of the ankle-foot-orthosis (T2) were compared using paired sampled t-tests. Based on gait variability scores at T1, a high and low gait variability group was determined, and change scores in the functional gait parameters were compared using non-parametric independent sampled t-tests. A significance level of p < 0.1 was used. Findings: No significant differences in step length, walking speed and energy cost of walking between T1 and T2 were found (p > 0.20). Step length increased more in people with high gait variability scores at T1 compared to those with low gait variability scores (High: +3.1 [-3.2 - +6.91, Low: +0.2 [-6.8 - +3.71 cm, p = 0.085), while no differences between groups were found for walking speed and energy cost of walking (p > 0.129). Interpretation: After provision of stiffness-optimized ankle-foot-orthoses in people with bilateral calf muscle weakness, no functional gait adaptations were found. However, people demonstrating high gait variability increased step length more compared to those demonstrating lower variability, which might be an indication that variability plays a role in adaptation.