Effect of hip abduction assistance on metabolic cost and balance during human walking

The use of wearable robots to provide walking assistance has rapidly grown
over the last decade, with significant advances made in robot design and
control methods toward reducing physical effort while performing an
activity. The reduction in the walking effort has mainly been achieved by
assisting forward progression in the sagittal plane. Human gait, however,
is a complex movement that combines motions in three planes, not only the
sagittal but also the transverse and frontal planes. In the frontal plane,
the hip joint plays a key role in gait, including balance. However,
wearable robots targeting this motion have rarely been investigated. In
this study, we developed a hip abduction assistance wearable robot by
formulating the hypothesis that assistance that mimics the biological hip
abduction moment or power could reduce the metabolic cost of walking and
affect the dynamic balance. We found that hip abduction assistance with a
biological moment second peak mimic profile reduced the metabolic cost of
walking by 11.6% compared to the normal walking condition (p=0.009). The
assistance also influenced balance-related parameters, including the
margin of stability. Hip abduction assistance influenced the
center-of-mass movement in the mediolateral direction. When the robot
assistance was applied as the center of mass moved toward the opposite
leg, the assistance replaced some of the efforts that would have otherwise
been provided by a human. This indicates that hip abduction assistance can
reduce physical effort during human walking while influencing balance.