Purpose: The aim of this study was to determine the effects of inspiratory muscle training (IMT) on exercise tolerance, inspiratory muscle fatigue, and the perception of dyspnea in asthmatic individuals.
Methods: Using a matched double-blind placebo-controlled design, 15 clinically diagnosed asthmatic individuals underwent either 6 wk of IMT (n = 7) consisting of 30 breaths twice daily at 50% maximum inspiratory pressure (PI max) or sham-IMT (placebo; PLA, n = 8) consisting of 60 breaths daily at 15% PI max. Time to the limit of exercise tolerance (Tlim) was assessed using constant-power output (70% peak power) cycle ergometry. Inspiratory muscle fatigue was determined by comparing the pre- to postexercise reduction in PI max. Dyspnea during the Tlim test was evaluated at 2-min intervals using the Borg CR-10 scale.
Results: There were no significant changes (P > 0.05) in Tlim, inspiratory muscle fatigue, or perception of dyspnea in the PLA group after the intervention. In contrast, in the IMT group, PI max increased by 28%, and Tlim increased by 16% (P < 0.05). Dyspnea during exercise was also reduced significantly by 16% (P < 0.05). The exercise-induced fall in PI max was reduced from 10% before IMT to 6% after IMT (P < 0.05), despite the longer Tlim. Pulmonary function remained unchanged in both the IMT and PLA groups.
Conclusions: These data suggest that IMT attenuates inspiratory muscle fatigue, reduces the perception of dyspnea, and increases exercise tolerance. These findings suggest that IMT may be a helpful adjunct to asthma management that has the potential to improve participation and adherence to exercise training in this group. However, the perception of breathlessness is also an important signal of bronchoconstriction, and thus, caution should be exercised if this symptom is abnormally low.