Objective: Insulin resistance in obese subjects results in the impaired use of glucose by insulin-sensitive tissues, e.g., skeletal muscle. In the present study, we determined whether insulin resistance in obesity is associated with an impaired ability of exercise to stimulate muscle blood flow, oxygen delivery, or glucose uptake.
Research methods and procedures: Nine obese (body mass index = 36 +/- 2 kg/m(2)) and 11 age-matched nonobese men (body mass index = 22 +/- 1 kg/m(2)) performed one-legged isometric exercise during hyperinsulinemia. Rates of femoral muscle blood flow, oxygen consumption, and glucose uptake were measured simultaneously in both legs using [(15)O]H(2)O, [(15)O]O(2), [(18)F]fluoro-deoxy-glucose, and positron emission tomography.
Results: The obese subjects exhibited resistance to insulin stimulation of glucose uptake in resting muscle, regardless of whether glucose uptake was expressed per kilogram of femoral muscle mass (p = 0.001) or per the total mass of quadriceps femoris muscle. At similar workloads, oxygen consumption, blood flow, and glucose uptake were lower in the obese than the nonobese subjects when expressed per kilogram of muscle, but similar when expressed per quadriceps femoris muscle mass.
Discussion: We conclude that obesity is characterized by insulin resistance of glucose uptake in resting skeletal muscle regardless of how glucose uptake is expressed. When compared with nonobese individuals at similar absolute workloads and under identical hyperinsulinemic conditions, the ability of exercise to increase muscle oxygen uptake, blood flow, and glucose uptake per muscle mass is blunted in obese insulin-resistant subjects. However, these defects are compensated for by an increase in muscle mass.