Graded Exercise Hypoxia Testing

"Participants will perform a graded exercise test on either a cycle ergometer or treadmill. The testing protocol will begin with a 5- 10 min warm-up of either cycling or running/walking at the participants preferred pace.~If the graded exercise test is on a bike, exercise will begin at wattage that elicits \~50% of their heart rate max, HRmax = 208 - 0.7 × age and increase by either 10W, 15W, or 20W every two minutes in a stepwise fashion until symptom limitation. The step of the wattage increase will be at the discretion of the investigators.~If the graded exercise test is on a treadmill, the test will begin at a speed that elicits \~50% of predicted HRmax. Following, the speed of the treadmill will increase 0.5 mph (0.8 km/hr) every two minutes in a stepwise fashion until symptom limitation. If the participant maxes out the speed of the treadmill, we will increase the grade 2% every 2-minutes until symptom limitation."

"Participants will perform a single constant work rate exercise tests during graded hypoxia. They will be outfitted with either a facemask or mouthpiece connected to a uni-directional breathing valve. During inspiration, subjects will breathe from a closed-system Douglas bag balloon reservoir (\~200 L) connected to the value on the inspired side via air-tight clean-bor tubing.~The participant will complete the same mode of exercise as they did during visit 1, either bike or treadmill. The resistance on the bike or incline of the treadmill will be set to elicit an intensity equivalent to \~50% of their V̇O2max determined during visit 1. Participants will complete 5-minute stages over a range of FiO2 values. The exercise test will begin in an FiO2=0.21 (i.e. room air). Following this first 5-min stage the FiO2 will increase to 0.25, afterwards, participants will complete another stage at FiO2=0.21 and then decrease in a stepwise fashion every 5-minutes."