Force Adaptation in Human Walking With Symmetrically Applied Downward Forces on the Pelvis

The application of external constraints and/or applied forces during movement can lead to reactive as well as adaptive changes in human motion. Previous research has shown adaptation in walking kinematics when external forces were applied to a leg. This work aims to study adaptation in human walking when externally applied forces were present on the pelvis during the swing and stance phases of both legs. A novel tethered pelvic assist device (TPAD) was used to passively apply symmetric downward forces on the human pelvis while walking. During the experiment, eight healthy subjects walked on a treadmill at a constant speed while their kinematics and foot pressure data were recorded. Data analysis revealed that the healthy subjects exhibited both reactive as well as adaptive changes in their gait parameters. The immediate response of the subjects was to increase their hip flexion to clear their foot off the ground as they were unable to lift their pelvis to their usual height in the presence of downward forces. Seven out of eight subjects resisted the downward forces to move their pelvis up. Eventually, they reached a level of downward force that they could sustain over the training session. This adaptation to the downward force was reflected in the heel peak pressure values during the cycles of the gait. On removing the tethers, aftereffects in heel peak pressure values were observed as a result of higher magnitude of pelvic acceleration in vertical direction. In summary, symmetrically applied external forces on the pelvis of healthy subjects resulted in reactive changes in the gait kinematics and adaptive changes in the gait kinetics and the foot interaction forces with the ground.