Postural instability measures have been extensively studied to understand the prevalence and cause of trips and falls in the elderly. While not as prevalent, middle-aged adults also have shown an increase in trips and falls, specifically down stairs. Measuring lateral deviation of plantar pressure and foot clearance in middle-aged adults, in conditions encountered in daily life, could provide insight into this phenomenon. The purpose of this study was to compare plantar pressure deviation and foot clearance in healthy middle-aged men and women during stair descent under two lighting conditions, normal and low level light.

Using 27 subjects, plantar pressure and foot clearance were measured on four steps under normal and low light. Subjects, randomized into two groups in a reversal design of the lighting conditions, showed significant increases in lateral deviation on right steps 1 and 2 under low light, within each group. Group 2 had a significantly higher variability on step 1 than group 1. Foot clearance remained statistically similar irrespective of lighting condition, and group 1 foot clearance under low light was significantly higher than normal.

In middle-age adults, this study found a trend towards increased lateral plantar pressure deviation while walking down stairs under low light. Along with the lack of increased foot clearance, this indicates a possible degradation of compensatory postural stability changes in the middle-aged adult. Further studies using more steps, darker conditions and analyzing joint angles and moments could provide greater insight into declines in postural stability factors in the middle-aged adult.