Longitudinal Changes in Postural Stability in Older Adults: An Exploratory Comparison of Two Community-Based Physical Activity Cohorts

Postural stability is an important component of functional health in older adults; however, longitudinal observations from routine community physical activity programs remain limited. This exploratory secondary observational analysis compared changes in postural stability between two archival cohorts of University of the Third Age participants assessed over different observation periods. The dataset comprised 48 paired assessment records representing 43 unique participants. Five individuals appeared in both historical datasets; therefore, the primary independent comparison included 24 participants in the longer-observation cohort and 19 in the shorter-observation cohort. The respective intervals between baseline and follow-up assessments were 408–568 and 21–76 days. The cohorts corresponded to programs offering 77 and eight scheduled physical activity sessions, respectively, although individual attendance was not documented. Postural stability was assessed using the HUMAC Balance System under two 30-s firm-surface conditions with eyes open and eyes closed. Ten outcomes were evaluated using Wilcoxon signed-rank tests for within-cohort changes and Mann–Whitney U tests for between-cohort differences in change scores, with Holm adjustment for multiple comparisons. No outcome changed significantly in the longer-observation cohort after adjustment. In the shorter-observation cohort, the eyes-closed sway index and eyes-closed stability score (ECSS) changed in a less favorable direction (Holm-adjusted p = 0.043 and p = 0.048, respectively). Between-cohort differences in change were significant for both outcomes (Holm-adjusted p = 0.019 for each; rank-biserial correlations −0.553 and 0.557, respectively). Sensitivity analyses using alternative strategies to exclude overlapping records retained the statistical significance of these findings. The results demonstrate differences in selected eyes-closed postural stability measurements between archival cohorts; however, scheduled activity exposure and follow-up duration were inseparable. Consequently, the findings do not establish an independent effect of exercise duration or preservation of postural control attributable to physical activity. Prospective studies with comparable observation intervals and verified individual exercise exposure are required to determine their clinical significance.