Age-Related Associations Between Relative Handgrip Strength and Body Composition in Women with Obesity

Background: Relative muscular function has emerged as a clinically relevant marker of muscle quality and health in obesity. However, limited evidence is available regarding age-related associations between relative handgrip strength and body composition outcomes in women with obesity. Methods: This cross-sectional study included 419 female outpatients with obesity (age range 18–80 years). Participants were stratified into age groups according to sample distribution. Body composition was assessed using Body Mass Index (BMI), waist circumference (WC), fat mass percentage (FM%), fat-free mass (FFM%), and waist-to-height ratio (WHtR). Relative handgrip strength (relative HST) was assessed together with balance performance (M-BESS), lower-body functional performance (5STS), and movement quality (FMS CS). Kruskal–Wallis analyses were performed for all functional measures. Age-stratified linear regressions and pooled models including relative HST × age-group interaction terms were used to examine associations with body composition outcomes; whole-sample models were additionally adjusted for age and physical activity level (IPAQ-SF). Results: Significant differences across groups were observed for BMI (p = 0.0006), FM% (p = 0.0308), relative HST (p = 0.0002), M-BESS score (p < 0.0001), and 5STS performance (p < 0.0001). Relative HST was significantly associated with lower FM% and higher FFM% across all age groups. In addition, significant associations with lower WC were observed in middle-aged and older women. However, pooled interaction analyses provided no evidence that the associations between relative HST and FM%, FFM%, WC, or WHtR differed significantly across age groups (p of all interactions > 0.29). Conclusions: Relative HST was associated with body composition outcomes across different age groups of women with obesity, but the strength of these associations did not differ significantly by age group. These findings suggest that relative HST may provide clinically relevant information beyond traditional anthropometric measures. However, prospective studies are needed to determine its potential clinical utility in individualized, person-centered obesity management.