Influence of Graded Hypercapnia on Endurance Exercise Performance

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.

Inclusion criteria

• Male or female, age 18-45
• In good health as determined by medical screening
• Passed his/her most recent Army Combat Fitness Test (ACFT) (Military Volunteers Only) or performs aerobic exercise at least 2 times per week and able to complete two mile run in ≤ 21 minutes (Civilian Volunteers)
• Willing to not participate in any exercise or drink alcoholic beverages for 24 hours before each study visit.
• Willing to not take part in any strenuous exercise in the 36 hours before each visit.
• Willing not to drink caffeine or eat food until after testing on familiarization and performance testing visits (visits 2-6).
• Willing to maintain a similar dietary pattern in the 2 days before each familiarization and performance visits.
• Have supervisor approval if permanent party military or a federal employee at U.S. Army Natick Soldier System Center
• Able to speak and read English fluently

Exclusion criteria

• Females who are pregnant or planning to become pregnant during the study
• Taking dietary supplements, prescriptions, or over the counter medication, other than a contraceptive (unless approved by medical staff & PI)
• Musculoskeletal injuries that compromise ability to run on a treadmill
• Abnormal blood count, presence of abnormal blood chemicals (hemoglobin S or sickle cell traits)
• Smokers or tobacco/nicotine users (unless have quit > 1 month prior)
• Any history of asthma
• Current or recent respiratory tract or sinus infections (< 1 month prior)
• Allergy to skin adhesive
• Any history of migraine or recurrent headaches
• Any history of panic disorder
• Blood donation in the previous 8 weeks
• Positive Covid-19 test within the last month