Fig. 1.

Study schematic. A: β-adrenergic receptor (AR) blockade was verified in 3 subjects using a graded isoproterenol (Iso) infusion to raise heart rate (HR) and blood pressure (BP); then propranolol (Prop) was infused during cycling, and isoproterenol infusion was repeated at 1 h postexercise. B: 6 subjects completed 2 trials with propranolol or saline infusion during cycling followed by stable isotope infusion and muscle biopsies.