Increase in carbon dioxide accelerates the performance of endurance exercise in rats.

Endurance exercise generates CO via aerobic metabolism; however, its role remains unclear. Exogenous CO by transcutaneous delivery promotes muscle fibre-type switching to increase endurance power in skeletal muscles. Here we determined the performance of rats running in activity wheels with/without transcutaneous CO exposure to clarify its effect on endurance exercise and recovery from muscle fatigue. Rats were randomised to control, training and CO groups. Endurance exercise included activity-wheel running with/without transcutaneous CO delivery. Running performance was measured after exercise initiation. We also analysed changes in muscle weight and muscle fibres in the tibialis anterior muscle. Running performance improved over the treatment period in the CO group, with a concomitant switch in muscle fibres to slow-type. The mitochondrial DNA content and capillary density in the CO group increased. CO was beneficial for performance and muscle development during endurance exercise: it may enhance recovery from fatigue and support anabolic metabolism in skeletal muscles.