Previous difficulty with lidocaine (xylocaine) will be an exclusion. To be eligible for these studies, volunteers must be free of clinical evidence of cardiac, renal, hepatic, and vascular disease, or other major medical problems that would endanger the volunteers or compromise the scientific validity of the studies. Subjects with a history of myocardial infarction, proteinuria (defined as 1+ protein), alcohol or drug abuse, malignancy or neuromuscular disease will be excluded. Subjects who have gained or lost more than 3 kg during the past 3 months will be excluded. Because of the PET, MR, and DEXA scanning, all premenopausal women must have a negative pregnancy test within 24 hours prior to these procedures. To avoid radiation exposure of the infant, women who are currently breastfeeding will not be permitted to participate in this research study. Subjects will be excluded if they have a contraindication to MRI such as surgical or vascular implants, pregnancy, pacemaker, or claustrophobia. In subjects with a questionable history of metallic fragments, an X-ray of the suspected area of the body will be performed to rule such out.