Aerobic Fitness: The subject's aerobic fitness will be determined based on the results from a stress test. All stress tests will be conducted by a cardiac research nurse. In brief, subjects will perform a graded exercise test (Bruce treadmill protocol) where speed and inclination of the treadmill increase every 3 minutes. The subject will be asked to exercise to volitional fatigue. Cardiac function will be monitored with a 12 lead ECG. The ECG data also will be used to determine if there is any evidence of cardiac disease (e.g. arrhythmia). Predictive equations developed for men and women will be used to calculate the subject's peak oxygen uptake. This value will represent the subject's aerobic fitness.