Locomotor adaptations for changes in the slope of the walking surface.

The goal of this study was to examine the transition of walking from a level surface onto different inclined surfaces. Kinematic data of limb and trunk segments were recorded from individuals as they approached and stepped onto four different ramped surfaces (slopes= 3 degrees , 6 degrees , 9 degrees , 12 degrees ). This transition introduced significant adaptations to the swing limb trajectory that were evident in even the lowest ramp condition and appear to be scaled to the ramp inclination although the nature of this scaling seemed to change between the 6 degrees and 9 degrees conditions. An increased forward pitch of the trunk orientation during all ramp conditions was initiated early on during the preceding stance phase on level ground. The swing limb modification essentially consisted of a two-stage response. The initial response of the limb trajectory changes was not specific to the degree of inclination but later changes were dependent on the ramp condition. The initial response is to ensure a safe toe clearance as the foot approaches the edge of the ramp and then later modifications provide the appropriate positioning of the limb to prepare for an elevated foot contact. Early changes were actively produced through an increased pull-off by the hip flexors and an elevation of the swing limb by the active muscle control of the stance limb. Ankle dorsiflexion also appears to have a supporting role increasing toe clearance. Absorption at the hip and knee during later swing contribute to control and position the limb in preparation for foot contact. These strategies were similar to those adopted for step changes in the level of the walking surface where there are similar demands of the quickly moving the limb forward and upward, however, the positioning of the limb for new angled landing surface requires further adaptations.