The purpose of this study was to investigate the relationship between excess CO2 output during and after short duration-intensive exercise and skeletal muscle characteristics (i.e., muscle fiber type, muscle capillary density and muscle buffering capacity). Twelve healthy males (age; 22.4±2.9 years, height; 172.3±5.8 cm, weight; 65.0±4.8 kg) performed 30-s maximal cycle ergometer sprinting. ExcessCO2 output during and after exercise was obtained through respiratory gas analysis. ExcessCO2 output per unit of time (ExcessCO2) was calculated by subtracting O2 from CO2 during and after exercise. Muscle biopsy samples were taken from the right vastus lateralis muscle, and then muscle fiber type, muscle capillary density and muscle buffering capacity were measured. ExcessCO2 calculated as the sum of ExcessCO2 from the onset of exercise until 15 min after exercise was not significantly correlated with any muscle fiber types, while it was significantly correlated with capillary-to-fiber ratio (r = 0.791, P < 0.01). A significant negative correlation was also demonstrated between ExcessCO2-to-La peak ratio and muscle buffering capacity (r = -0.645, P < 0.05). These results suggest that ExcessCO2 during and after short duration-intensive exercise is affected by the amount of H+ buffered by nonbicarbonate system and the amount of H+ diffusion from muscle to blood depending on the development of muscle capillaries.
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