Under researched somatosensory contributions to postural stability, in addition to high incident rates of foot injury in the physically active population, lead to two investigative studies. An initial research study compared variables of two postural stability assessment devices to determine reliability of outcome measures and commonality of outcome measures to dynamic postural control. A second study assessed which measures of postural stability were effective in differentiating between injured persons using foot orthotics and non-injured persons, and also compared effects of 3-month foot orthotic usage on measures of postural stability among three groups. In the first study, 23 healthy subjects tested on two separate occasions one-week apart, counterbalancing the testing order. Intraclass correlation coefficients (ICC) and Pearson product moment correlations were calculated and analyzed. In the second study, 15 patients diagnosed with plantar fasciitis or medial arch sprain were given custom orthotics and matched with 15 non-injured subjects given custom orthotics, and 15 healthy control subjects on gender, age, height, and body mass index. All 45 subjects were assessed on five postural stability tests (12 dependent variables) on seven occasions over a four-month period. Repeated measures MANOVA was employed to evaluate group, time and interaction effects for the outcome variables (α=0.05). Test-retest reliability, in the first study, ranged from moderate to high (ICC[subscript 2,1]=0.71 to 0.92) for all outcome measures. Pearson correlations revealed four statistically significant relationships (p< .05) between outcome measures (r=0.43 to -0.72). In the second study, nine variables were entered into repeated measures MANOVA demonstrating significant main and interaction effects. Post hoc univariate analyses demonstrated six variables with group main effects and three variables with time main effects. Interaction effects in post hoc analysis were non-significant. The moderate to high test-retest reliability observed for outcome measures in the first study is encouraging. Correlations between device outcome measures, while statistically significant, were low enough to suggest that each device provided unique information regarding postural stability. Results from the second study provide strong evidence that foot orthotic wear affects postural stability over time. The nature of test protocols suggests that functional postural stability testing aids in assessing effectiveness of foot orthotics. / Graduation date: 2002