The effects of surface slope on multi-segment foot kinematics in healthy adults

Previous work evaluating the effects of surface slope on gait has focused on lower extremity kinematics and kinetics. However, an assessment of multi-segment foot kinematics during walking on inclined and declined ramps has not been previously reported. Sagittal ankle motion using a single rigid body foot model and three-dimensional hindfoot and forefoot kinematics for 24 healthy adults (16 females and 8 males, average age 25.5 ± 4.4 years) were compared during level surface, inclined surfaces of 3%, 6%, 9% and 12% grade and a declined surface of approximately 7.5% grade at a constant speed using a standard treadmill. Significant differences in peak hindfoot plantarflexion, sagittal plane range of motion and time of peak dorsiflexion, plantarflexion, varus and valgus were seen between surface slope conditions. Significant changes were also seen in forefoot plantarflexion and sagittal plane range of motion however the maximum difference between conditions was less than 3°. These results indicate that foot mechanics can be significantly altered when ambulating on ramps in healthy adults. Specifically, treadmill protocols which incorporate different surface slopes often encountered during ambulation of daily living, may provide an improved technique in evaluating a patient's ability to function in the community.