Men and women, 35-45 yrs: lean (BMI< 25), with normal blood sugars. Research project examining how fat stored in the muscles affects insulin activity. Two days of testing at the Clinical Translational Research Center, Anschutz Medical Campus Exclusions: serious health problems, smoking, taking hormones or medicine to lower glucose. PI: Bryan Bergman, PhD, COMIRB #10-0443, 5/27/2011