Associations Between Physical Fitness Components and Metabolic Syndrome in middle-aged adults: A Cross-Sectional Study Using Relative Strength Indicators and ROC Analysis

Zhanfei Zheng^1,2*Haoliang Qing³Zhang Lf⁴Changyuan Duan^2,5*

• ¹Sports Coaching College, Beijing Sport University, Beijing, China
• ²Department of Sports Science, Wenzhou Medical University, WenZhou, China
• ³Wenzhou University School of Physical Education and Health, Wenzhou, China
• ⁴Department of Physical Education, Sichuan Electronic and Mechanic Vocational College, Mianyang, China
• ⁵Department of Physical Education, Gangneung-Wonju National University, Gangneung-si, Republic of Korea

Metabolic syndrome (MetS) is a major risk factor for cardiovascular disease and type 2 diabetes, particularly in middle aged populations. Physical fitness, especially muscular strength and cardiorespiratory capacity, has emerged as a pragmatic indicator of metabolic health. ThisIn this cross-sectional study, we investigated the association between multiple fitness components and the presence of MetS in middle aged adults, with emphasis on weight normalized indices. Methods: A total of 570 middle aged adults (369 men, 201 women) were enrolled in a cross-sectional study. Assessments included body composition by bioelectrical impedance (appendicular skeletal muscle mass, ASM), handgrip strength, isokinetic lower limb strength at 60°/s using HUMAC NORM, and cardiorespiratory fitness by maximal treadmill testing (VO₂max, mL·kg⁻¹·min⁻¹, Bruce protocol). MetS was defined by International Diabetes Federation criteria. Within each sex, logistic regression models (scaled per 1 SD decrease in each exposure; Model 1 adjusted for age; Model 2 adjusted for age and BMI) quantified associations, and receiver operating characteristic analyses with the Youden index identified sex specific cut offs. Results: Participants with MetS showed significantly lower relative grip strength, relative lower limb strength, and VO₂max than their non MetS counterparts. Lower ASM ratio was also characteristic of MetS. In age adjusted models, decreased ASM ratio and relative grip strength were associated with higher odds of MetS, with attenuation after additional adjustment for BMI. ROC analysis yielded pragmatic thresholds for identifying MetS: ASM ratio < 24.0% in men and < 20.0% in women; relative grip strength < 53.3 in men and < 38.0 kg/BW in women; relative lower limb strength < 5.94 in men and < 5.03 Nm/BW in women; VO₂max < 24.0 in men and < 19.3 mL·kg⁻¹·min⁻¹ in women. Conclusions: Weight normalized fitness indices, particularly ASM ratio and relative grip This is a provisional file, not the final typeset article strength, are informative for identifying prevalent MetS in middle aged adults and support sex specific screening thresholds suitable for clinical and community practice.