Subjects will need to come to the Substrate Metabolism Laboratory in the morning around 7:00 AM. After about a 15-30 minute rest, the study team will collect a blood sample from the subject's hand or forearm. The study team will also obtain a small sample of fat tissue from the area just underneath the skin near the belly button. Next, subjects will exercise on a treadmill at a moderate intensity for about 1 hour. Immediately after exercising the study team will collect a blood sample. The subject will remain resting in the laboratory for 3 hours after exercise, and then the study team will collect another blood and fat tissue sample. Upon completion, the subject will be provided a snack before leaving the laboratory.

Subjects will exercise on a treadmill for 1 hour at a moderate intensity (approximately 70% of their predicted VO2peak).

The stromovascular fraction will be isolated from subcutaneous lipo-aspirate samples by collagenase digestion and a series of filtration/wash steps (routinely performed by our lab). This isolation protocol has been optimized to yield the minimum number of stromal cells required to identify and recover the following cell populations by fluorescence-activated cell sorting (FACS), listed as cell surface stain = cell type: CD64+/CD11c+ = macrophages

FACS will be performed at the University of Michigan Flow Cytometry Core, and sorted cells will be recovered for subsequent gene expression analysis using the StepOnePlus real time PCR system (Life Technologies) with fluorescent probe-based assays.

The stromovascular fraction will be isolated from subcutaneous lipo-aspirate samples by collagenase digestion and a series of filtration/wash steps (routinely performed by our lab). This isolation protocol has been optimized to yield the minimum number of stromal cells required to identify and recover the following cell populations by fluorescence-activated cell sorting (FACS), listed as cell surface stain = cell type: CD34+/CD31+ = endothelial cells

FACS will be performed at the University of Michigan Flow Cytometry Core, and sorted cells will be recovered for subsequent gene expression analysis using the StepOnePlus real time PCR system (Life Technologies) with fluorescent probe-based assays.