Comparability of self-reported and accelerometer-based physical activity assessment in patients with facioscapulohumeral muscular dystrophy

Background Quantifying physical activity (PA) is clinically relevant in facioscapulohumeral muscular dystrophy (FSHD). Wearable accelerometers provide objective measures, whereas self-reported questionnaires are a widely used, cost-effective alternative. However, their comparability in FSHD remains unclear. Hence, the objective of this work is to evaluate the comparability between self-reported PA, assessed by the International Physical Activity Questionnaire (IPAQ) long form, and accelerometer-derived measures, obtained with Fibion SENS, in FSHD patients. Methods Participants wore Fibion SENS for seven consecutive days and completed the IPAQ for the same period. Sitting time (ST), walking time (WT), moderate-intensity activity time (MAT), vigorous-intensity activity time (VAT), and total activity time (TAT) were compared between methods. Differences, associations, and agreement were assessed using Wilcoxon signed-rank tests, Spearman correlation analyses, and Bland–Altman analyses, respectively. Statistical significance was set at p < .05. Clinically assessed disease severity and fatigue were included as potential confounders in adjusted association analyses. Results Fifty-three patients with FSHD (mean age 45.89 ± 15.46 years; 23 females, 30 males; median clinical score 5) were included. Compared with Fibion SENS measures, IPAQ significantly underestimated ST, WT, and TAT, while overestimating MAT and VAT. Associations were generally absent and, when detected, were weak, with only TAT showing a significant unadjusted association (ρ = 0.309). Bland–Altman analyses demonstrated wide limits of agreement across domains, with proportional bias observed for ST, MAT, and TAT. Conclusion Overall, IPAQ showed limited comparability with accelerometer-based measurements in the analyzed cohort. These methods should therefore not be considered interchangeable but rather complementary, with device-based measures capturing the amount of activity and self-reported measures providing information on perceived effort and the subjective and contextual aspects of daily-life activities. Their combined use may provide a more comprehensive characterization of PA in individuals with FSHD.