Increased metabolic insulin sensitivity related to reductions in fasting glucose (r = -0.41, p = 0.025), VO<sub>2</sub>max (r = 0.55, p = 0.002), fasting leptin (r = -0.54, p = 0.01), and weight loss (r = -0.60, p < 0.001) after exercise and placebo, but not exercise and metformin.<h4>Conclusions</h4>Metformin attenuated metabolic insulin sensitivity and insulin-stimulated carbohydrate oxidation after high-intensity exercise training in adults at risk for MetS. Here, LEP is linked to metabolic syndrome.