Associations between physical fitness components and metabolic syndrome in middle-aged adults: a cross-sectional study using relative strength indicators and ROC analysis.

Participants with MetS showed significantly lower relative grip strength, relative lower-limb strength, VO₂max, and ASM ratio than their non-MetS counterparts.

• Sample included 570 middle-aged adults (369 male, 201 female) assessed in a cross-sectional design.
• MetS was defined according to International Diabetes Federation criteria.
• Body composition was measured by bioelectrical impedance analysis; grip strength, isokinetic lower-limb strength at 60°/s (HUMAC NORM system), and VO₂max (Bruce protocol treadmill testing) were assessed.
• All fitness measures were weight-normalized (relative indices) to allow comparison across body sizes.

Decreased ASM ratio and lower relative grip strength were associated with higher odds of MetS in age-adjusted models, with attenuation after additional adjustment for BMI.

• Logistic regression was scaled per 1 SD decrease in each exposure.
• Model 1 adjusted for age; Model 2 adjusted for age and BMI.
• Associations for ASM ratio and relative grip strength were statistically significant in Model 1 but attenuated in Model 2 after BMI adjustment.
• Analyses were conducted separately within each sex.

ROC analysis identified sex-specific thresholds for ASM ratio to identify prevalent MetS.

• Optimal ASM ratio cutoff was <24.0% in male individuals and <20.0% in female individuals.
• Cutoffs were identified using the Youden index from receiver operating characteristic analyses.
• These thresholds are described as 'pragmatic' for clinical and community screening practice.

ROC analysis identified sex-specific thresholds for relative grip strength to identify prevalent MetS.

• Optimal relative grip strength cutoff was <53.3 kg/BW in male individuals and <38.0 kg/BW in female individuals.
• Cutoffs were derived using the Youden index.
• Relative grip strength was among the most informative fitness indicators for MetS identification alongside ASM ratio.

ROC analysis identified sex-specific thresholds for relative lower-limb strength to identify prevalent MetS.

• Optimal relative lower-limb isokinetic strength cutoff was <5.94 Nm/BW in male individuals and <5.03 Nm/BW in female individuals.
• Lower-limb strength was measured at 60°/s using the HUMAC NORM isokinetic dynamometry system.
• Cutoffs were identified using the Youden index from ROC analyses.

ROC analysis identified sex-specific thresholds for VO₂max to identify prevalent MetS.

• Optimal VO₂max cutoff was <24.0 mL·kg⁻¹·min⁻¹ in male individuals and <19.3 mL·kg⁻¹·min⁻¹ in female individuals.
• Cardiorespiratory fitness was assessed by maximal treadmill testing using the Bruce protocol.
• Cutoffs were identified using the Youden index from ROC analyses.

The study investigated multiple physical fitness components in relation to MetS with particular emphasis on weight-normalized indices in middle-aged adults.

• A total of 570 middle-aged adults (369 male, 201 female) were enrolled.
• Fitness components assessed included appendicular skeletal muscle mass (ASM ratio), handgrip strength, isokinetic lower-limb strength, and cardiorespiratory fitness (VO₂max).
• Cross-sectional study design was used; causal inference is therefore limited.
• Sex-stratified analyses were conducted throughout.