The influence of solid ankle-foot-orthoses on forward propulsion and dynamic balance in healthy adults during walking.

BACKGROUND In post-stroke hemiparetic subjects, solid polypropylene ankle-foot-orthoses are commonly prescribed to assist in foot clearance during swing while bracing the ankle during stance. Mobility demands, such as changing walking speed and direction, are accomplished by accelerating or decelerating the body and maintaining dynamic balance. Previous studies have shown that the ankle plantarflexors are primary contributors to these essential biomechanical functions. Thus, with ankle-foot-orthoses limiting ankle motion and plantarflexor output during stance, execution of these walking subtasks may be compromised. This study examined the influence of a solid polypropylene ankle-foot-orthosis on forward propulsion and dynamic balance in healthy adults. METHODS Kinematic and kinetic data were recorded from 10 healthy adults walking with and without a unilateral ankle-foot-orthosis at steady-state slow (0.6m/s) and moderate (1.2m/s) speeds, and during accelerated (0-1.8m/s at 0.06m/s(2)) and decelerated (1.8-0m/s at -0.06m/s(2)) walking. Propulsion was quantified by propulsive and braking impulses (i.e., time integral of the anterior-posterior ground reaction force) while dynamic balance was quantified by the peak-to-peak range of whole-body angular momentum. FINDINGS The propulsive impulses decreased in the leg with ankle-foot-orthosis compared to the contralateral leg and no ankle-foot-orthosis condition. Further, the ankle-foot-orthosis resulted in a greater range of angular momentum in both the frontal and sagittal planes, which were correlated with the reduced peak hip abduction and reduced ankle plantarflexor moments, respectively. INTERPRETATION Solid ankle-foot-orthoses limit the successful execution of important mobility subtasks in healthy adults and that the prescription of ankle-foot-orthosis should be carefully considered.