Childhood Muscular Fitness Phenotypes and Adult Metabolic Syndrome

Purpose: The objective of this study is to determine whether childhood muscular fitness phenotypes (strength, endurance, and power) are independently associated with adult metabolic syndrome (MetS). Methods: We conducted a longitudinal study including 737 participants who had muscular fitness measures in 1985 when age 9, 12, or 15 yr and attended follow-up in young adulthood 20 yr later when measures of MetS were collected. Childhood measures of muscular fitness included strength (right and left grip, leg, and shoulder extension and flexion), endurance (number of push-ups in 30 s), and power (distance of a standing long jump). A muscular fitness score was created using all individual muscular fitness phenotypes. In adulthood, waist circumference, blood pressure, HDL cholesterol, triglycerides, and glucose were measured. Adult outcomes were MetS defined using the harmonized definition and a continuous MetS risk score. Results: Participants with childhood muscular strength, muscular power, and combined muscular fitness score in the highest third had significantly lower relative risk (RR) for MetS and a lower continuous MetS score in adulthood independent of cardiorespiratory fitness than those in the lowest third (strength: RR = 0.21 (0.09, 0.49) A = -0.46 (-0.59, -0.34) power: RR = 0.26 (0.12, 0.60), A = -0.36 (-0.49, -0.23) fitness score: RR = 0.20 (0.09, 0.47), beta = -0.45 (-0.58, -0.33)). However, adjustment for childhood waist circumference reduced the effect sizes for both adult outcomes by 17%-60%. Conclusion: Phenotypes of childhood muscular fitness can be used to predict adult MetS independent of cardiorespiratory fitness. Although a large proportion of the effect of childhood muscular fitness on adult MetS is potentially being mediated by child waist circumference, these data suggest that promotion of muscular fitness among children might provide additional protection against developing adult MetS.