Reliability and Validity of Ratings of Perceived Difficulty During Performance of Static Standing Balance Exercises

Standardized instruments for measuring the intensity of balance exercises in clinical environments are lacking. The objective of this study was to develop a method for quantifying the perceived intensity of standing balance exercises. A test-retest study design was used, with repeated evaluations within the same visit and between visits 1 week later. Sixty-two participants who were healthy and 18 to 85 years old (with a mean age of 55 years [SD = 20 years]; 50% women) were enrolled. On each of 2 visits, they performed 2 sets of 24 randomized static standing exercises consisting of combinations of the following factors: surface, vision, stance, and head movement. Postural sway was measured with an inertial measurement unit, and ratings of perceived difficulty (RPD) were recorded using numerical and qualitative scales. The RPD scales were validated against the quantitative sway measures using a general linear model approach. The test-retest reliability of the RPD scales was examined using a weighted kappa coefficient. Both RPD scales were associated with postural sway measures with correlation coefficients > 0.6 for the whole sample. The test-retest reliability of the ratings varied considerably across the different balance exercises, and the highest weighted kappa values occurred for RPD scores on the numerical scale within the second visit, as moderate agreement was achieved in 18 of the 24 exercises. The limitations are that the RPD scales need to be validated for other types of balance exercises and in individuals with balance disorders. The RPD scores correlated with the magnitude of postural sway, suggesting that they can be used as a proxy measure of perceived intensity of balance exercises.