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 over a one-month period. Free exercise performance & total hemoglobin mass testing. Compensation of $10/hour ($90 for completion of study). If interested, e-mail benjamin.ryan@colorado.edu.