The purpose of this study is to provide the first integrated examination of the interaction between muscle insulin action and exercise-stimulated muscle glucose uptake in obesity from the whole body to the cellular/molecular level.

Inclusion Criteria:

For the exercise studies of leg glucose uptake - "insulin sensitive" group:

• Sedentary, normal weight, premenopausal women.
• Sedentary, age-matched normal weight men.
• Weight stable for two (2) months prior to study.
• Willing to provide written, informed consent.
• For the exercise studies of leg glucose uptake - "insulin resistant" group:

For the exercise studies of leg glucose uptake - "insulin resistant" group:

• Upper body obese (UBO) premenopausal women.
• Age-matched upper body obese (UBO) men.
• Weight stable for two (2) months prior to study.
• Willing to provide written, informed consent.

Exclusion Criteria:

• Age < 18 or > 55 years (premenopausal women and age-matched men).
• Use of glucose-lowering agents.
• For female subjects: positive pregnancy test at the time of enrollment or study
• History of prior upper abdominal surgery such as adjustable gastric banding, pyloroplasty and vagotomy.
• Active systemic illness or malignancy.
• Symptomatic macrovascular or microvascular disease.