Reliability of COP-based postural sway measures and age-related differences

Area of Science:

• Biomechanics and Motor Control
• Gerontology
• Human Movement Science

Background:

• Postural sway assessment using center of pressure (COP) is crucial for understanding balance.
• Reliability of COP measures is essential for accurate clinical interpretation and research.
• Age-related differences in postural control and the reliability of its measures are not fully understood.

Purpose of the Study:

• To evaluate the within-day and between-day reliability of various COP-based postural sway measures.
• To investigate age-related differences in the reliability of these COP measures.
• To guide the selection and interpretation of COP measures in research and clinical practice.

Main Methods:

• Thirty-two healthy participants (16 younger, 16 older) underwent COP recording during quiet stance over four days.
• Measures included mean velocity, median power frequency, RMS distance, sway area, and fractal analyses (HR/S, DFA).
• Reliability was quantified using Intraclass Correlation Coefficient (ICC) and Standard Error of Measurement (SEM).

Main Results:

• Mean velocity demonstrated the highest reliability among all tested COP measures.
• Detrended Fluctuation Analysis (DFA) exponents showed better relative reliability than Hurst Rescaled Range (HR/S) exponents.
• Within-day reliability generally surpassed between-day reliability for most measures.
• Older adults exhibited superior relative reliability (ICC) across most COP measures compared to younger adults.
• Absolute reliability (SEM) was comparable between age groups, with exceptions for mean velocity and sway area.

Conclusions:

• Mean velocity is a highly reliable measure for assessing postural sway.
• DFA offers a more reliable fractal analysis for postural sway than HR/S.
• Understanding age-related reliability differences is vital for accurate interpretation of postural control data.