Participants will undergo baseline measurements of pulmonary function and maximal oxygen uptake (VO2max). They will then complete two familiarization trials, with 10 minutes of submaximal exercise (~40%VO2max) followed by a self-paced 2-mile treadmill time trial. Lastly, they will complete three experimental trials, repeating the same submaximal and time-trial exercise procedures while breathing the test gas (0%, 2%, or 4% CO2-all with normal 21% oxygen). During the experimental trials, arterialized capillary blood samples will be collected at rest breathing room air, at rest breathing the test gas, and during submaximal exercise at 40% VO2max breathing the test gas. The primary outcome is 2-mile treadmill time-trial performance. Secondary outcomes include ventilation, metabolic rate, heart rate, arterialized capillary pH/PCO2/HCO3, perceived exertion, dyspnea, leg discomfort, breathing descriptors, and headache ratings.
The aim of this randomized, single-blind, placebo-controlled crossover trial is to determine the effects of graded hypercapnia (0, 2, and 4% inspired CO2) on endurance performance. Twelve healthy and fit young adults (men and women) will complete this study. Participants will perform experimental trials on 3 separate days (one each breathing 0%, 2%, and 4% inspired CO2-all with normal 21% oxygen). During each trial, they will perform 10 minutes of submaximal treadmill walking exercise and then complete a self-paced 2-mile treadmill run time-trial.