IRS1 and Insulin resistance: Stuart et al. found a significant decrease in the number of type I muscle fibers, more than two-fold increase in the number of type II muscle fibers, and a 60% decrease in whole-body insulin responsiveness, according to the results of lateral thigh muscle biopsies from a large number of patients with insulin resistance,these effects were not proportional to the decrease in the levels of insulin receptor (IRS1) and glucose transporter (GLUT4), indicating that the decrease in the number of type I muscle fibers plays a key role [97].