Resistance exercise stimulates mixed muscle protein synthesis in lean and obese young adults

Obese individuals exhibit a diminished muscle protein synthesis response to nutrient stimulation when compared with their lean counterparts. However, the effect of obesity on exercise-stimulated muscle protein synthesis remains unknown. Nine lean (23.5 ± 0.6 kg/m² ) and 8 obese (33.6 ± 1.2 kg/m² ) physically active young adults participated in a study that determined muscle protein synthesis and intracellular signaling at rest and following an acute bout of resistance exercise. Mixed muscle protein synthesis was determined by combining stable isotope tracer ([¹³ C₆ ]phenylalanine) infusion with serial biopsies of the vastus lateralis. A unilateral leg resistance exercise model was adopted so that resting and postexercise measurements of muscle protein synthesis could be obtained simultaneously. Obesity was associated with higher basal levels of serum insulin (P < 0.05), plasma triacylglycerol (P < 0.01), plasma cholesterol (P < 0.01), and plasma CRP (P < 0.01), as well as increased insulin resistance determined by HOMA-IR (P < 0.05). However, resting and postexercise rates of muscle protein synthesis were not significantly different between lean and obese participants (P = 0.644). Furthermore, resistance exercise stimulated muscle protein synthesis (~50% increase) in both groups (P < 0.001), with no difference between lean and obese (P = 0.809). Temporal increases in the phosphorylation of intracellular signaling proteins (AKT/4EBP1/p70S6K) were observed within the exercised leg (P < 0.05), with no differences between lean and obese. These findings suggest a normal anabolic response to muscle loading in obese young adults.