Self-reported Home Exercise Adherence: A Validity and Reliability Study Using Concealed Accelerometers

Accurate measurement of adherence to prescribed exercise programs is essential. Diaries and self-report rating scales are commonly used, yet little evidence exists to demonstrate their validity and reliability.

To examine the concurrent validity of adherence to home strengthening exercises measured by (1) exercise diaries and (2) a self-report rating scale, compared to adherence measured using an accelerometer concealed in an ankle cuff weight. Test-retest reliability of the self-report rating scale was also assessed.

In this clinical measurement study, 54 adults aged 45 years or older with self-reported chronic knee pain were prescribed a home quadriceps-strengthening program. Over 12 weeks, participants completed paper exercise diaries and, at appointments every 2 weeks, rated their adherence on an 11-point numeric rating scale. A triaxial accelerometer was concealed in the ankle cuff weight used for exercises. Self-reported adherence rating scale data over each 2-week period were analyzed using descriptive statistics, the Wilcoxon signed-rank test, and a Bland-Altman plot to assess agreement, Spearman correlations for validity, and intraclass correlation coefficients for test-retest reliability.

Exercise adherence was significantly overestimated in diaries during the 12 weeks (diary median, 220 exercises; accelerometer, 176; P<.001) and was moderately correlated with accelerometer data (r = 0.52; 95% confidence interval: 0.26, 0.69). A Bland-Altman plot indicated large between-participant variability in agreement between these measures. Self-reported adherence showed poor to fair correlations with accelerometer data (mean r = 0.23-0.39), and less than acceptable reliability (intraclass correlation coefficient = 0.79; lower 1-sided 95% confidence limit, 0.68).

Exercise diaries showed questionable validity and variable levels of agreement compared with accelerometer-measured exercise completion. A self-reported adherence rating scale had limited validity and less than acceptable test-retest reliability. J Orthop Sports Phys Ther 2018;48(12):943-950. Epub 27 Jul 2018. doi:10.2519/jospt.2018.8275.