Alterations in fatty acid mobilization and oxidation may be primary adaptations responsible for the improvements in metabolic health after a single session of endurance exercise. The investigators will determine the effect of a single session of endurance exercise on whole-body fatty acid mobilization and oxidation, IMTG concentration and the expression of factors that regulate these processes in skeletal muscle of 11 women with abdominal obesity (age: 18-45y). In addition, the investigators will evaluate how these factors, and exercise, effect insulin signalling and insulin sensitivity. Every effort will be made to recruit subjects from ethnic and minority groups. Before participating in the study, subjects will be informed of all the procedures and potential risks, and they will sign an informed consent form approved by The University of Michigan Institutional Review Board. Eligible volunteers will participate in three separate trials, in a randomized order. In two trials subjects will eat exactly the same amount of calories, except in one trial they will exercise (eucaloric + exercise) and in the other trial they will remain sedentary (hypercaloric). In a third trial subjects will again remain sedentary but instead they will ingest appropriate calories to maintain caloric balance (eucaloric + sedentary). By doing this the investigators are also able to investigate the effect of acute caloric perturbations on insulin sensitivity, because it is possible that the enhanced insulin sensitivity evident after exercise, as compared to the sedentary state, is due to caloric deficit and not the exercise bout, per se.

Inclusion Criteria:

• Premenopausal; Body mass index 30-40 kg/m2; Waist circumference >88 cm

Exclusion Criteria:

• Evidence of metabolic or cardiovascular disease; Pregnancy; Hyperlipidemia (fasting plasma triglyceride concentration > 150 mg/dl); Hematocrit < 34%; Undertaking regular exercise (i.e., >2 times/week)