Relationship between the phase angle from bioelectrical impedance analysis and daily physical activity in patients with rheumatoid arthritis

Objectives: This study aimed to examine the relationship between daily physical activity and the phase angle (PhA) obtained by bioelectrical impedance analysis in rheumatoid arthritis (RA) patients. Methods: Data from a prospective cohort study of RA patients who were surveyed every year were analysed. The PhA was assessed by the bioelectrical impedance analysis method, and physical activity was assessed as the amount of time of exercise in metabolic equivalents (METs) per day using a triaxial accelerometer for 7 consecutive days. The association between physical activity and the PhA was evaluated using the isotemporal substitution model in multiple regression analysis. Results: Seventy-six RA patients were included in the analysis (81% female and age 66.2 +/- 13.1 years). On cross-sectional analysis, the isotemporal substitution model in multiple regression analysis showed that the PhA was 0.05 points higher every 10 minutes when activities with intensity of 1 <= METs < 2 were replaced by activities with intensity of >= 3 METs (P =.01). Over 1 year, the rate of change in the PhA was 0.69% higher every 10 minutes when activities with intensity of 1 <= METs < 2 were replaced by activities with intensity of >= 3 METs (P =.037). Conclusion: The PhA in RA patients may be related to physical activity level.