Does Regional Muscle Distribution Predict Functional Capacity? Sex-Specific Insights from Bioimpedance and Performance Testing

Background: The relationships between segmental body composition and multidimensional performance outcomes remain insufficiently characterized in adults with limited but regular physical activity. This study examined associations between body composition parameters and functional test performance, while identifying sex-based differences. Methods: Forty-seven adults (31 women, 16 men; age 48.04 ± 11.33 years) underwent segmental bioelectrical impedance analysis and functional assessments including handgrip strength, isometric plank endurance, and single-leg balance. Correlations and sex comparisons statistical tests were performed. Results: Strong positive correlations were observed between segmental muscle mass and handgrip strength (r = 0.74–0.84, p < 0.05), with moderate associations for plank endurance (r = 0.30–0.32, p < 0.05). Fat mass demonstrated inverse relationships with performance, particularly for plank endurance (r = −0.36 to −0.62, p < 0.05). Males exhibited significantly greater muscle mass (p < 0.01), superior handgrip strength (p < 0.01), and longer plank times (p = 0.01). Females presented higher fat mass in lower limbs (p < 0.01). Conclusions: Segmental muscle mass shows strong associations with strength and moderate associations with core endurance, while adipose tissue exhibits inverse relationships. Pronounced sexual dimorphism exists in both body composition and functional capacity.