PPARGC1A and Insulin resistance: Several studies show that in addition to improving performance, HIIT improves glucose metabolism, increases mitochondrial biogenesis, activity of respiratory chain and β-oxidation, and also the expression of GLUT4 and PGC-1α–all of which cause deterioration of insulin resistance (Burgomaster et al., 2005, 2008; Helgerud et al., 2007; Talanian et al., 2007; Daussin et al., 2008).