The traditional view of mitochondria as isolated, spherical, energy producing organelles is undergoing a revolutionary transformation. Emerging data show that mitochondria form a dynamic networked reticulum that is regulated by cycles of fission and fusion. The discovery of a number of proteins that regulate these activities has led to important advances in understanding human disease. Data show that activation of dynamin related protein 1 (Drp1), a protein that controls mitochondrial fission, is reduced following exercise in prediabetes, and the decrease is linked to increased insulin sensitivity and fat oxidation. The proposed research will test the hypothesis that mitochondrial dynamics is a key mechanism of insulin resistance in type 2 diabetes. Translational first-in-man studies will use an acute lipid challenge to investigate the physiological significance of altered skeletal muscle mitochondrial dynamics on insulin sensitivity in humans. The experimental approach harnesses innovative molecular and cellular tools, interfaced with physiologically significant human studies to obtain meaningful data on insulin resistance, and has the potential to generate insights that will lead to new diabetes therapies for future generations.