Prolonged Isocapnic Buffering and Economical Breathing in Trained Distance Runners

To compare ventilatory equivalents, end-tidal gas pressures, breathing pattern, and the duration of the isocapnic buffering phase between trained and recreationally trained distance runners, and to determine how buffering duration relates to breathing pattern.

In this cross-sectional study, twenty-four 1500-m runners (12 trained: age 21.4 ± 2.0 years, body mass 58.5 ± 5.5kg, height 171.5 ± 7.2cm, body fat 15.6 ± 3.9%; 12 recreationally trained: age 21.5 ± 1.0 years, body mass 57.1 ± 7.7kg, height 166.6 ± 8.0cm, body fat 15.0 ± 2.9%; six men and six women per group) performed a continuous incremental treadmill ramp test (0.5km·h⁻¹ increase every 30s) to volitional exhaustion with breath-by-breath pulmonary gas-exchange measurement. We compared ventilatory equivalents, end-tidal gas pressures at the gas exchange threshold, respiratory compensation point, peak exercise breathing pattern, and isocapnic-buffering duration between groups and across exercise stages.

Trained runners showed a lower minimum ventilatory equivalent for oxygen (24.70 ± 2.37 vs 28.58 ± 1.73; P < 0.001) and for carbon dioxide (28.06 ± 2.24 vs 31.39 ± 2.38; P = 0.002), whereas the ventilatory equivalent for carbon dioxide slope did not differ (P = 0.609). End-tidal oxygen pressure was lower and end-tidal carbon dioxide pressure higher in trained runners at all three stages (both P < 0.001), although the magnitude of the end-tidal carbon dioxide difference varied by sex and stage (P < 0.001). The isocapnic buffering phase lasted longer in trained runners (3.46 ± 0.46 vs 1.79 ± 0.39min; P < 0.001; partial η² = 0.82) and was positively associated with mean tidal volume (r = 0.981) and inversely with mean breathing frequency (r = -0.905; both P < 0.001).

Trained distance runners combine lower ventilatory equivalents with a deeper, slower breathing pattern and a markedly longer isocapnic buffering phase. Buffering duration may therefore index the ventilatory strategy adopted during progressive exercise.