Sex Differences in the Prevalence of Metabolic Syndrome Based on Leg Strength, Cardiorespiratory Fitness, and Skeletal Muscle Mass in Elderly

Background: Metabolic syndrome (MetS) is characterized by abdominal obesity, high blood glucose, and dyslipidemia. Low fitness, muscle mass, and strength increase the risk of MetS. The characteristics of these variables are highly interrelated. This cross-sectional study aimed to analyze the prevalence of MetS by combining leg strength (LSTR), cardiorespiratory fitness (CRF), and appendicular skeletal muscle mass (ASM) in elderly men and women. Methods: Participants included 1420 persons aged 65–79 years (men: 753, women: 667). An isokinetic dynamometer was used to measure LSTR; CRF was evaluated by measuring maximum oxygen uptake; and ASM was assessed using bio-impedance analysis. The measured CRF, LSTR, and ASM were converted to relative values by dividing by body weight and grouped into ‘high’ and ‘low’ based on the median value. The diagnosis of MetS was based on five criteria: waist circumference, blood pressure, high-density lipoprotein cholesterol, triglycerides, and fasting glucose. MetS was diagnosed when the participant fulfilled 3 or more of the criteria, and odds ratios (ORs) were analyzed using logistic regression. Results: MetS was diagnosed in 32.1% and 30.3% of men and women, respectively. The relative LSTR and ASM values were significantly higher in the non-MetS group compared to those of the MetS group in both sexes. The OR for MetS in men was 3.6-fold higher in the low LSTR group, 3.5-fold higher in the low CRF group, and 2.3-fold higher in the low ASM group than in the high groups. In women, the OR for MetS increased 1.3-fold in the group with low LSTR and 3.7-fold in the group with low CRF. The OR for MetS exhibited a 3.5-fold increase in men and a 2.4-fold increase in women for combined low LSTR and low ASM compared to those of the combined high LSTR and high ASM group. Despite high ASM, the OR for MetS was a 3.5-fold higher in men and a 3.9-fold in women for low LSTR and low CRF group. Conclusions: The prevalence of MetS increased in elderly with relatively decreased LSTR, ASM and decreased CRF. Furthermore, the prevalence of MetS is increased when both LSTR and ASM are low despite high CRF. In addition, even if ASM was low, the risk of metabolic syndrome did not increase when both CRF and LSTR were high. In conclusion, when two or more of the three variables CRF, LSTR, and ASM were low, the prevalence of MetS increased.