 Specific Objectives: 1.Develop an appropriate graded calf exercise test protocol for evaluating perfusion and metabolism during exercise in subjects with peripheral arterial disease PAD, 2.compare perfusion in gastroc-soleus and tibialis anterior muscles during exercise and recovery from exercise, and to compare metabolism in those muscles during exercise, 3.compare the perfusion during exercise and recovery between groups with and without PAD, and to compare metabolism during exercise between groups with and without PAD, 4.estimate sample sizes and effect sizes for a future clinical trial to determine the efficacy of walking and calf muscle exercise training for improving calf muscle perfusion and metabolism. 5.determine the sensitivity and specificity of the PET exercise test in classifying subjects into groups with or without PAD, and 6. determine the test-retest reliability coefficients of perfusion and metabolic measures. 