Lower-extremity muscle quality asymmetry in older adult fallers and non-fallers: a phase angle analysis

Falls in older adults are a major public health concern associated with significant morbidity, psychological distress, and functional decline. Although lower-limb strength asymmetry is an established risk factor for falls, whether muscle quality asymmetry is associated with falls remains unclear. Phase angle (PhA), derived from multi-frequency bioelectrical impedance analysis (MF-BIA), is a validated biomarker of muscle quality. Therefore, this study aimed to compare segmental muscle quality and asymmetry between older adults with a recent history of falls ("fallers") and their non-falling counterparts ("non-fallers"), and to evaluate its association with fall-related outcomes.

This study included 120 community-dwelling older adults, divided into non-fallers (n = 60; median age 69.5 years) and fallers (n = 60; median age 70.0 years). Participants completed fear of falling evaluations, physical performance tests (including chair stand and Timed Up and Go tests), and MF-BIA measurements. Segmental impedance (Z) at six frequencies (1, 5, 50, 250, 500, and 1,000 kHz) and reactance (Xc) at three frequencies (5, 50, and 250 kHz) were measured for the arms, legs, and trunk.

Compared to non-fallers, fallers exhibited significantly poorer sit-to-stand performance (p = 0.03) and a higher percentage of whole-body fat (p = 0.01). No significant group differences were found for fear of falling or Timed Up and Go. While overall segmental PhA did not differ between groups, fallers showed significantly greater PhA asymmetry at 5 kHz in both the arms (p = 0.02) and legs (p = 0.02). Crucially, only leg PhA asymmetry was positively correlated with fall status at 5 kHz (r_s = 0.29, p = 0.03) and negatively correlated with sit-to-stand performance at 5 kHz (r_s = -0.32, p = 0.01) and 50 kHz (r_s = -0.34, p = 0.04).

Muscle quality asymmetry in the lower extremities, identified by PhA asymmetry at 5 kHz, is modestly associated with fall status and reduced lower-limb performance in older adults. These findings suggest that leg PhA asymmetry may serve as an adjunctive outcome measure for assessing fall risk in geriatric populations.