The Applied Exercise Science Lab is recruiting male subjects (ages 18-30) for a study looking at how breathing low levels of carbon monoxide (CO) affects the total amount of hemoglobin in the body and whether this affects cardiovascular fitness and exercise performance. -The experiment will consist of 20 visits that will take a total of nine hours duration over a one-month period. -Compensation of $10/hour ($90 for study completion) If interested, please contact Benjamin Ryan at benjamin.ryan@colorado.edu.