Inclusion Criteria:  55 years and older, 18-40 years old Healthy, physically active, performing at least 90 min/week of physical activity Free of physical limitations that may interfere with alterations in daily physical activity levels  Exclusion Criteria:  Physician diagnosed metabolic disease, HIV, hepatitis, or tuberculosis. Body weight change of greater than 5% within the previous 2 months Smoking within the previous 2 months. Taking medications that alter blood glucose levels