Respiratory responses and isocapnic buffering phase in child and youth soccer players during an incremental exercise test

This study investigated the respiratory response and isocapnic buffering (IB) phase during an incremental exercise test to exhaustion in 16 child soccer players (11.9±0.9 years) and 18 youth soccer players (18.2±2.9 years). The IB phase was calculated as the difference in oxygen uptake (VO2) between the respiratory compensation point (RCP) and metabolic threshold (MT) and expressed in either absolute or relative values. The maximal oxygen uptake (VO ) was higher in youth players than in child players. For youth players, VO was measured at 55.9 ± 3.6 mL min kg and 74.9 ± 4.8 mL min kg , while for child players, VO was 50.8 ± 4.1 mL min kg and 67.2 ± 6.1 mL min kg ( < 0.001). MT and RCP occurred at 69.8 ± 6.7% and 90.9 ± 6.9% of VO in child players and at 73.9 ± 5.1% and 91.5 ± 4.5% of VO in youth players, respectively. The two groups had no significant difference (p > 0.05). Absolute IB (10.6 ± 2.8 vs 9.7 ± 3.1 mL min kg ), relative IB (23.1 ± 5.7 vs 19.1 ± 6.1), and the ratio of RCP VO to MT VO (1.3 ± 0.09 vs 1.24 ± 0.09) were similar in child and youth players ( > 0.05). There was no difference in minute ventilation (V̇E, mL min kg ) and respiratory exchange ratio during exercise between the two groups ( > 0.05). During exercise, respiratory frequency, ventilatory equivalent for carbon dioxide (VE/VCO ) and oxygen (VE/VO ), VE/VCO slope, end-tidal O pressure were higher in child players than in youth players, while tidal volume (L kg ), O pulse, and end-tidal CO pressure were lower (p < 0.05). Despite differences in aerobic capacity and ventilatory response to exercise, child players showed similar IB phase as youth players. Although child players have lower ventilation efficiency than youth players, the higher ventilation response for a given VCO may provide an advantage in regulating acid-base balance during intense exercise.