Figure 2. Five-hour isotope infusion protocol. Beginning between 5 and 7 am, subjects in the continuously fed state were infused with a prime-constant d₅-phenylalanine isotope. Indocyanine green dye concentration was measured between hours 3 and 4 to determine leg blood flow. Femoral arteriovenous sampling during the fifth hour measured cross-leg phenylalanine balance. Muscle biopsies were performed at 2 and 5 hours while subjects were under intravenous conscious sedation.