Foot placement alters the mechanisms of postural control while standing and reaching

This study investigated the effects of altering foot placement on the strategies used by able-bodied subjects to perform reaching tasks while standing. The motivation for this study was to consider the results in the context of a person with a spinal cord injury using a functional neuromuscular stimulation (FNS) system to stand while reaching. Three foot placement conditions were compared as subjects reached to the left, right, and center. Centers of pressure (COP), joint angles, and joint moments were calculated as postural parameters using force platform and video marker data. Side-by-side and wide foot placements resulted in similar postural parameters. In contrast, the modified tandem stance (feet spaced at pelvic width with one foot shifted forward) resulted in anterior/posterior COP excursions that were larger in magnitude and more consistent across reach directions when compared to the other foot placement conditions. Furthermore, the movement patterns used during the tandem stance were more consistent and may be more readily achievable with FNS than the movement patterns utilized with the side-by-side and wide stances. These results suggest that the modified tandem stance may enhance the functionality of FNS standing systems and may also be useful in other standing rehabilitation programs.