Am. J. Respir. Crit. Care Med.,
Volume 156, Number 1, July 1997, 116-121
The Relationship Between Maximal Expiratory Flow
and Increases of Maximal Exercise Capacity with
Exercise Training
TONY G.
BABB,
KELLY A.
LONG,
and
JOSEPH R.
RODARTE
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas; The University of Texas Southwestern
Medical Center, Dallas; Department of Human Performance, Rice University, Houston; and Department of Medicine,
Baylor College of Medicine and The Methodist Hospital, Houston, Texas
We previously reported that patients with mild to moderate airflow limitation have a lower exercise
capacity than age-matched controls with normal lung function, but the mechanism of this reduction
remains unclear (). Although the reduced exercise capacity appeared consistent with deconditioning, the patients had altered breathing mechanics during exercise, which raised the possibility that
the reduced exercise capacity and the altered breathing mechanics may have been causally related.
Reversal of reduced exercise capacity by an adequate exercise training program is generally accepted
as evidence of deconditioning as the cause of the reduced exercise capacity. We studied 11 asymptomatic volunteer subjects (58 ± 8 yr of age [mean ± SD]) selected to have a range of lung function
(FEV1 from 61 to 114% predicted, with a mean of 90 ± 18% predicted). Only one subject had an FEV1
of less than 70% predicted. Gas exchange and lung mechanics were measured during both steady-state and maximal exercise before and after training for 30 min/d on 3 d/wk for 10 wk, beginning at
the steady-state workload previously determined to be the maximum steady-state exercise level that
subjects could sustain for 30 min without exceeding 90% of their observed maximal heart rate (HR).
The training workload was increased if the subject's HR decreased during the training period. After
10 wk, subjects performed another steady-state exercise test at the initial pretraining level, and another maximal exercise test. HR decreased significantly between the first and second steady-state exercise tests (p < 0.05), and maximal oxygen uptake (
O2max) and ventilation increased significantly
(p < 0.05) during the incremental test, indicating a training effect. However, the training effect did
not occur in all subjects. Relationships between exercise parameters and lung function were examined by regression against FEV1 expressed as percent predicted. There was a significant positive correlation between O2max percent predicted and FEV1 percent predicted (p < 0.02), and a negative correlation between FEV1 and end-expiratory lung volume (EELV) at maximal exercise (p < 0.03).
There was no significant correlation between FEV1 and maximal HR achieved during exercise; moreover, all subjects achieved a maximal HR in excess of 80% predicted, suggesting a cardiovascular limitation to exercise. These data do not support the hypothesis that the lower initial O2max in the subjects with a reduced FEV1 was due to deconditioning. Although increased EELV at maximal exercise,
reduced O2max, and a reduced O2max response with training are all statistically associated with a reduced FEV1, there is no direct evidence of causality.
