  Preferred walking speed is a widely-used performance measure for people with
mobility issues, but is usually measured in straight line walking for fixed
distances or durations. However, daily walking involves walking for bouts of
different distances and walking with turning. Here, we studied walking for
short distances and walking in circles in unilateral lower-limb amputees
wearing an above or below-knee passive prosthesis, specifically, a Jaipur foot
prosthesis. Analogous to earlier results in non-amputees, we found that their
preferred walking speeds are lower for short distances and lower for circles of
smaller radii. Using inverse optimization, we estimated the cost of changing
speeds and turning such that the observed preferred walking speeds in our
experiments minimizes the total energy cost. The inferred costs of changing
speeds and turning were much larger than for non-amputees. These findings could
inform prosthesis design and rehabilitation therapy to better assist changing
speeds and turning tasks in amputee walking. Further, measuring the preferred
speed for a range of distances and radii is a more robust subject-specific
measure of walking performance.
