influence of graded hypercapnia on endurance exercise performance

Conditions: Hypercapnia

Summary: 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.

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.

Eligibility criteria:
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