Breathing during exercise in subjects with mild-to-moderate airflow obstruction: effects of physical training

In this study we explored the effects of physical training on the response of the respiratory system to exercise. Eight subjects with irreversible mil d-to-moderate airflow obstruction [forced expiratory volume in 1 s of 85 +/ - 14 (SD) % of predicted and ratio of forced expiratory volume in 1 s to fo rced vital capacity of 68 +/- 5%] and six normal subjects with similar anth ropometric characteristics underwent a 2-mo physical training period on a c ycle ergometer three times a week for 31 min at an intensity of similar to 80% of maximum heart rate. At this work intensity, tidal expiratory flow ex ceeded maximal flow at control functional residual capacity [FRC; expirator y flow limitation (EFL)] in the obstructed but not in the normal subjects. An incremental maximum exercise test was performed on a cycle ergometer bef ore and after training. Training improved exercise capacity in all subjects , as documented by a significant increase in maximum work rate in both grou ps (P < 0.001). In the obstructed subjects at the same level of ventilation at high workloads, FRC: was greater after than before training, and this w as associated with an increase in breathing frequency and a tendency to dec rease tidal volume. In contrast, in the normal subjects at the same level o f ventilation at high workloads, FRC was lower after than before training, so that tidal volume increased and breathing frequency decreased. These fin dings suggest that adaptation to breathing under EFL conditions does not oc cur during exercise in humans, in that obstructed subjects tend to increase FRC during exercise after experiencing EFL during a 2-mo strenuous physica l training period.