This study aimed to investigate the characteristics of static postural control across three age groups: the ultra-elderly (90+ years), the elderly (under 90), and middle-aged adults using frequency analysis, in particular direction-specific differences.
A total of 57 participants were enrolled in this study: 24 middle-aged adults (age 36.8 ± 5.4), 19 elderly individuals (age 81.2 ± 6.8), and 14 ultra-elderly individuals (age 96.5 ± 4.1). Participants stood quietly on a force platform for 30 seconds under both eyes-open and eyes-closed conditions. Postural stability was evaluated using center of pressure (COP) indicators, including the 95% confidence ellipse area, mean velocity on the horizontal plane, and root mean square (RMS) measurements in both AP and ML directions. The Romberg ratio of these indicators was also calculated. Additionally, power spectral density (PSD) and sample entropy of COP signal in the AP and ML directions were assessed, with frequency bands categorized as Ultra low (under 0.10 Hz), Very low (0.10-0.39 Hz), Low (0.39-1.56 Hz), and Moderate (1.56-6.25 Hz). Data analysis employed the Kruskal-Wallis test for differences in postural stability indicators, with post-hoc analysis via Steel-Dwass test where significant effects were identified. Statistical significance was set up to p 0.05.
The Romberg ratio for mean velocity on the horizontal plane was significantly higher in the elderly group compared to middle-aged participants (p = 0.02) but not when compared to the ultra-elderly (p = 0.24). No significant main effects were found for direction-specific linear indicators. However, a significantly smaller PSD in the moderate frequency band was observed in the middle-aged group compared to both elderly and ultra-elderly groups in the AP direction during both eye conditions (eyes-open, elderly: p = 0.03, ultra-elderly: p 0.01; eyes-closed, elderly: p 0.01, ultra-elderly: p 0.01). Additionally, the elderly group showed significantly smaller PSD in the moderate frequency band in the ML direction when eyes were open compared to the middle-aged group (p = 0.01). The middle-aged group also had significantly lower sample entropy in the AP direction compared to both elderly and ultra-elderly groups in both visual conditions (eyes-open, elderly: p = 0.03, ultra-elderly: p = 0.01; eyes-closed, elderly: p 0.01, ultra-elderly: p 0.01).
In both the elderly and the ultra-elderly, an increase in irregularity of postural control in the AP direction and a heightened dependence on somatosensory input have been suggested. This implies that while somatosensory capabilities decline, the increased reliance on them contributes to postural instability in older adults.
Effective interventions for postural control in the elderly should incorporate balance training that prioritizes sensory weighting considerations.
ultra-elderly
frequency analysis
