Alterations in pulmonary function following exercise are not caused by the work of breathing alone

Both pulmonary function and respiratory muscle strength decrease following exercise in healthy humans. The alterations in respiratory muscle are not the same following exercise and voluntary isocapnic hyperpnea that simulates that exercise. Therefore, in this study we measured pulmonary and respiratory muscle function following maximal exercise or hyperpnea that simulated the ventilation seen during exercise. Forced vital capacity (FVC), forced expiratory volume in 1 sec (FEV_1.0), maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP) and handgrip strength were measured before and following voluntary hyperpnea in which minute ventilation and breathing frequency were controlled to levels identical to those obtained during the exercise test, and before and following a period of rest of equal duration to the exercise and hyperpnea tests. FVC decreased by 400 ml (7%, p < 0.05) immediately post-exercise. MIP decreased by 12 mmHg (15%, p < 0.005) following exercise and remained depressed for 15 minutes. Neither MEP nor FEV_1.0 decreased following exercise, and none of the variables were altered following the control or hyperpnea bouts. These data indicate that pulmonary function and respiratory muscle strength are altered following exercise but not by similar bouts of hyperpnea without accompanying exercise. Therefore, exercise affects pulmonary function independent of the respiratory muscle work done.