Relationship between phase angle and lower-extremity function in older adults: Itabashi Longitudinal Study on Aging.

Objective: Evaluating muscle quality instead of its mass has gained attention in diagnosing sarcopenia. The aim of this study was to examine whether phase angle (PhA) as a bioelectrical impedance analysis (BIA)-derived muscle quality indicator is associated with overall lower extremity function better than appendicular skeletal muscle mass index (ASMI) in community-dwelling older adults.

Methods: This cross-sectional study used data from the Itabashi Longitudinal Study on Aging, a community-based cohort study. A sex-stratified multivariate logistic regression analysis was conducted using PhA and ASMI as exposures, and low physical function defined as short physical performance battery score <10 as the outcome, adjusted for age, being overweight, knee pain, and non-communicable diseases. Discrimination of low physical function was compared using the receiver operating characteristic curve.

Results: This study included 1464 participants (age 76 [73-80] y; 757 women), with 58 men (8%) and 66 women (9%) exhibiting low physical function. The multivariate odds ratio (OR; 95% confidence interval [CI]) for low physical function among the highest quartile, compared with the lowest quartile were significant in PhA in multiple sites (e.g., OR, 0.09; 95% CI, 0.03-0.32] for men and 0.12; 95% CI, 0.04-0.33 for women in the left leg) but not in ASMI (OR, 0.51; 95% CI, 0.19-1.34 for men and 0.56; 95% CI, 0.21-1.47 for women). Legs and whole-body PhA outperformed the ASMI in discriminating low physical function (P < 0.001).

Conclusion: PhA reflected physical function better than ASMI; using PhA instead of ASMI in BIA-based morphometric evaluation may add information on low physical function and enhance the diagnostic value of sarcopenia.