Specific Aim 1. The first specific aim is to develop the triple-tracer PET method for quantitative determinations of tissue perfusion, glucose transport and glucose phosphorylation in skeletal muscle. To measure blood flow and tissue perfusion, we will use 15O-H2O (half-life ~ 2 min; also referred to as 15O-water). To measure glucose transport, we will use 11C-3-O-methyl glucose (half-life ~ 20 min; also referred to as 3-0-MG), an analog that is transported but not phosphorylated or otherwise metabolized. 18F-2-deoxy-2-fluoro-glucose (half-life ~ 109 min; also referred to as FDG), will be used to examine glucose transport and glucose phosphorylation. Because of the differences in half-life of the three positrons (15O, 11C, and 18F), it is feasible to use each of these tracers, in sequence, in the same individual.