Subjects fasted overnight will receive primed constant intravenous (antecubital vein) infusions of stable isotope labelled amino acids for the duration of the study and blood samples will be taken from an arterial cannula and two femoral venous cannulae at regular intervals to quantify tracer enrichment and measure glucose uptake and insulin. In the first phase of the study, subjects' bulk femoral artery blood flow will be measured at 50, 70, 90 and 110 min by Doppler Ultrasound (USS). Nutritive blood flow will be measured in a defined area of the quadriceps in the control leg by Contrast Enhanced Ultrasound (CEUS) using the Phillips iU22 at 110 min. This involves a single intravenous administration of SonoVue® contrast agent. At 120 min the second phase of the study will begin with a dextrose and mixed amino acid intravenous infusion (antecubital vein) for the remainder of the study. Methacholine chloride (Provocholine®; Methapharm Inc.) in NaCl (0.9%, prepared by QMC pharmacy)will be infused (at 2-12 µg/min) into one femoral artery to double femoral artery flow at 150 min. Bulk femoral artery flow will again be measured (Doppler Ultrasound), this time in both legs at 170, 190, 210 and 230 min. Nutritive flow will be measured for a second time, in both legs by CEUS at 230 min. Four muscle biopsies (150-300 mg) of vastus lateralis will be taken according to the protocol and snap-frozen in liquid nitrogen.