Response of able-bodied persons to changes in shoe rocker radius during walking: Changes in ankle kinematics to maintain a consistent roll-over shape

Recent studies have determined a seemingly consistent feature of able-bodied level ground walking, termed the roll-over shape, which is the effective rocker (cam) shape that the lower limb system conforms to between heel contact and contralateral heel contact during walking (first half of the gait cycle). The roll-over shape has been found to be largely unaffected by changes in walking speed, load carriage, and shoe heel height. However, it is unclear from previous studies whether persons are controlling their lower limb systems to maintain a consistent roll-over shape or whether this finding is a byproduct of their attempt to keep ankle kinematic patterns similar during the first half of the gait cycle. We measured the ankle-foot roll-over shapes and ankle kinematics of eleven able-bodied subjects while walking on rocker shoes of different radii. We hypothesized that the ankle flexion patterns during single support would change to maintain a similar roll-over shape. We also hypothesized that with decrease in rocker shoe radii, the difference in ankle flexion between the end and beginning of single support would decrease. Our results supported these hypotheses. Ankle kinematics were changed significantly during walking with the different rocker shoe radii (p<0.001), while ankle-foot roll-over shape radii (p=0.146) and fore-aft position (p=0.132) were not significantly affected. The results of this study have direct implications for designers of ankle-foot prostheses, orthoses, walking casts/boots, and rocker shoes. The results may also be relevant to researchers studying control of human movements.