Low muscle fitness is associated with metabolic risk in youth.

Purpose: To examine the independent associations of muscle fitness and cardiorespiratory fitness with clustered metabolic risk in youth.

Methods: In 2005-2006, a cohort of 9- and 15-yr-olds (N = 2818) was randomly selected from all regions of Norway. The participation rate was 89% and 74% among the 9-and 15-yr-olds, respectively. We assessed muscular strength by measuring explosive, isometric, and endurance strength. Cardiorespiratory fitness was measured directly as peak oxygen uptake during a cycle ergometry test. Risk factors included in the composite risk factor score (sum of z-scores) were systolic blood pressure, triglyceride, high-density lipoprotein cholesterol, insulin resistance, and waist circumference.

Results: Muscle fitness was negatively associated with clustered metabolic risk, independent of cardiorespiratory fitness, and after adjustment for age, sex, and pubertal stage (beta = -0.112, P < 0.001). Independent of muscle fitness, an inverse association was found between cardiorespiratory fitness and clustered metabolic risk (beta = -0.337, P < 0.001). Moreover, the odds ratios for having clustered risk in the least fit quartile compared with the most fit quartile were 7.2 (95% confidence interval (CI)=4.3-12.0) and 17.3 (95% CI = 9.2-32.7) for muscle fitness and cardiorespiratory fitness, respectively.

Conclusions: Our results show that muscle fitness and cardiorespiratory fitness are independently associated with metabolic risk in youth.