VO2 Max: In Vivo Model for Functional Red Cell Testing. Can RECESS be Explained?

Inclusion Criteria: * Habitual exerciser defined as ≥ 30 minutes of at least moderate or high intensity exercise ≥ 3 times per week. After consent, and at the subsequent screening visit, a VO2 max test will be performed, and subjects with a low value (\< 35 mL/kg/min) will be excluded (screen failure). Based on our previous experience, we anticipate that \<10% of the subjects will fall into this category * Calculated total blood volume (TBV) ≥4,500 mL using an established formula: 1. Men: (0.006012 x H3) + (14.6 x W) + 604 = TBV 2. Women: (0.005835 x H3) + (15 x W) + 183 = TBV \[H=height in inches; W=weight in pounds\] * Has access to transportation to visit the blood collection facility and to return to Stony Brook for all study visits. Exclusion Criteria: * Any significant acute or chronic medical illness or problem, including, but not limited to, diabetes, hypertension, cardiac disease, asthma, chronic obstructive lung disease * Current or recent (last 60 days) tobacco or nicotine use * History of sickle cell trait or disease or any other acquired or hereditary hematological abnormality * History of fainting or other significant adverse reaction during phlebotomy or donation of blood * Known prolonged corrected QT interval (or evidence of such at screening) on electrocardiogram defined as \>470 ms * Known or suspected illicit drug or alcohol abuse * Known or suspected HIV, Hepatitis B, or Hepatitis C infection * History of thrombophilia or anticoagulant therapy * Pregnancy * Obesity defined as BMI\>30 * Recent history of blood donation: a) Single whole blood unit donation within the past 8 weeks; b) Double RBC donation by apheresis within the past 16 weeks; or c) Plasma donation by apheresis within the past 4 weeks * Inadequate RBC mass based on TBV \<4500 ml (above) or screening Hb \<14 g/dL