Acute transcutaneous CO2 exposure: A feasibility study for the future investigation of CO2-specific exercise adaptations.

Blood flow restricted (BFR) exercise induces musculoskeletal adaptations at reduced exercise loads. The role of hypercapnia during BFR remains unclear, due to difficulties in isolating this factor in vivo. We evaluated a hypercapnic model designed to raise CO₂ levels similar to low-intensity exercise, while minimizing other exercise-induced effects (e.g. hypoxia, lactate accumulation). In a crossover design, 18 participants were administered pure CO₂ (EXP) or room air (CON) transcutaneously from the neck down for 90 min. Ventilatory and blood markers (V̇CO₂, ETCO₂, V̇E, pH, and PCO₂) were measured throughout. The area under the curve of ETCO₂ was higher during EXP compared to CON (75.5 ± 83.7 vs. 32.8 ± 57.5 a.u., p = 0.05), confirming successful CO₂ administration. However, there was no significant effect on PCO₂ (p = 0.09), despite a trend toward reduced pH (p = 0.059). CONCLUSION: While transcutaneous CO₂ absorption induced a physiological response, the magnitude was small, and this model shows limited ecological validity to simulate exercise-like conditions.