Supplementary Material for: Sex-specific Differences in Ultrasound-Derived Muscle Parameters and Their Associations with Strength and Physical Function in Older Adults: A Systematic Review and Meta-Analysis

Background: Ultrasound technology is a promising tool for assessing muscle condition in older adults. However, sex-specific differences in how ultrasound-derived muscle parameters related to the physical function remain unclear.

Methods: A systematic search of PubMed, Web of Science, Embase, CINAHL, and SPORTDiscus was conducted to identify studies reporting sex-stratified associations between ultrasound-derived muscle parameters and functional measures. Correlation coefficients were transformed using Fisher’s z-transformation and analyzed with random-effects models, then back-transformed to Pearson’s r. Heterogeneity was assessed using the I2 statistic, and publication bias was evaluated using funnel plots and Egger’s test.
Results: Analysis of 39 studies revealed that ultrasound-derived muscle parameters were consistently correlated with strength assessments across sexes, including maximal and handgrip strength (males: muscle thickness [MT], r = 0.30–0.42; echo intensity [EI], r = -0.34 to -0.38; females: MT, r = 0.34–0.37; EI, r = -0.34 to -0.35; all p > 0.05). However, for explosive power, both MT and EI had stronger associations in males than females (MT: r = 0.70 vs. 0.42; EI: r = -0.52 vs. -0.27; both p < 0.05). In gait function, MT was positively correlated in females (r = 0.22, p < 0.05) but not in males (r = -0.03, p = 0.62). Additionally, EI correlations were significantly stronger in females than males in the Timed Up and Go (TUG) test (r = 0.40 vs. 0.19, p < 0.05).
Conclusions: This meta-analysis revealed that MT and EI exhibit comparable correlations with maximal and handgrip strength across sexes. However, both parameters show stronger associations with explosive power in males. In contrast, females displayed more robust associations with physical function, with MT being more strongly linked to gait speed and EI to TUG performance. These findings highlight the need for sex-specific considerations in ultrasound-based muscle evaluations and provide foundational data to inform future clinical applications.