Influence of brief carbon dioxide inhalation on acute exercise performance and recovery: A pilot study

Brief inhalation of carbon dioxide (CO₂) has been proposed to counteract transient hypocapnia by enhancing oxygen unloading, vasodilation, and sympathetic modulation. Despite these potential ergogenic mechanisms, CO₂ has rarely been investigated in the exercise context. The present study investigated whether brief CO₂ inhalation (iCO₂) influences performance and recovery during high-intensity interval exercise. Nine healthy adults completed two randomized, single-blinded crossover trials of repeated cycling intervals at 85% peak work rate until volitional exhaustion or cadence dropped below 60 rpm, with a minimum 2-min interval duration required and 3-min active recovery between bouts. Participants inhaled 5% CO₂ or room air (15 breaths) before and after each exercise bout. Gas exchange, cardiovascular responses, and perceived exertion were assessed. Total exercise time was similar between trials; however, participants completed more intervals with iCO₂. During the first interval, iCO₂ increased exercise duration and VO₂. At matched exercise time, perceived exertion and dyspnea were lower with iCO₂. During recovery, systolic blood pressure was lower and heart rate was higher following iCO₂. Brief iCO₂ improved first-interval performance, altered cardiovascular recovery, and reduced perceptual strain but did not extend overall exercise duration. These findings suggest iCO₂ may transiently modulate tolerance and autonomic-vascular responses during high-intensity interval exercise.