Objective. To investigate the relationship of muscular strength and cardiorespiratory fitness (CRF) to insulin resistance. Methods. In a cross sectional study of 126 volunteers (10'15 years) we measured insulin, glucose, lipids, body mass, height, waist circumference (WC), strength and CRF. Linear and logistic regression models assessed the relationships between these factors and estimated insulin resistance (Homeostasis Assessment Model2; HOMA2-IR). Results. Greater insulin resistance was associated with greater adiposity, lower CRF, and strength. Upper body strength and WC were the only independent predictors of insulin resistance, accounting for 39% of the variance (p < 0.001). Children in the highest and middle tertiles of absolute upper body strength were 98% less likely to have high insulin resistance than those with the lowest strength, adjusted for maturation and central adiposity, body mass (OR = 0.019; p = 0.003). Similar trends were present for high vs. low CRF. Conclusion. Muscular strength has been identified for the first time as an independent and powerful predictor of better insulin sensitivity in children. Lower strength, CRF and higher central adiposity are highly predictive of higher levels of insulin resistance in this cohort, and should be considered potential targets for interventions designed to enhance metabolic fitness in children and adolescents.