Imposed breathing pattern alters respiratory work during exercise.

Previous studies have shown the existence of an ideal respiratory rate (fR) for a given ventilation at which the respiratory work rate (J.s-1) is minimum. The purpose of the present study was to measure the effect of fR, tidal volume and breathing pattern on the respiratory work per breath and respiratory work rate during exercise on a cycle ergometer. Three work rates on the cycle ergometer were used and at each work rate the ventilation was kept constant. Two different breathing patterns were applied at each ventilation. Nine male trained cyclists [mean (SD) maximum oxygen consumption, 57 (5.47) ml.kg-1.min-1] participated in this study. The results indicated that there was a significant difference in the respiratory work per breath, with different breathing patterns at a given ventilation and for all levels of ventilation. There was no significant difference in the respiratory work rate with different breathing patterns at a given ventilation and for all levels of ventilation. In addition, the respiratory work per breath and respiratory work rate were increased with increasing ventilation. Thus, the data indicated that the manipulation of tidal volume, respiratory rate and breathing pattern had no significant effect on the energy cost of breathing for a given ventilation. The absence of this significant effect on respiratory work rate was observed across a range of ventilation from 24 to 72 l.min-1. These findings suggest that the breathing pattern is predominantly an expression of the function of the higher respiratory brain center instead of energy economy, at least within this range of ventilation.