V˙E Response to V˙CO₂ during Exercise Is Unaffected by Exercise Training and Different Exercise Limbs

Abstract

We designed two experiments to investigate the relationship between ventilation (V˙E) and CO₂ output (V˙CO₂) during exercise under the conditions of exercising different limbs, the arms as opposed to the legs (experiment 1), and of different physical training states after undergoing standard exercise training for 90 d (experiment 2). Six healthy young subjects underwent submaximal ramp exercise at an incremental work rate of 15 W/min for the arm and leg, and 11 healthy middle-aged subjects underwent an incremental exercise test at the rate of 30 W/3 min before and after exercise training. We measured pulmonary breath-by-breath V˙E, V˙CO₂, oxygen uptake (V˙O₂), tidal volume (VT), breathing frequency (bf), and end-tidal O₂ and CO₂ pressures (PETO₂, PETCO₂) via a computerized metabolic cart. In experiment 1, arm exercise produced significantly greater V˙E than did leg exercise at the same work rates, as well as significantly higher V˙O₂, V˙CO₂, and bf. The slopes of the regression lines in the V˙E–V˙CO₂ relationship were not significantly different: the values were 27.8 ± 2.1 (SD) during the arm exercise, and 25.3 ± 3.9 during the leg exercise, with no differences in their intercepts. In experiment 2, the V˙O₂, V˙CO₂, and V˙E responses at the same work rates were similar in both before and after the 90-d exercise training, whereas the heart rate (HR) and mean blood pressure (MBP) were significantly reduced after training. Exercise training did not alter the V˙E–V˙CO₂ relationship, the slope of which was 31.9 ± 4.9 before exercise training and 34.2 ± 4.4 after exercise training. We concluded that the V˙E–V˙CO₂ relationship during exercise is unaltered, independent of not only working muscle regions but also exercise training states.