Title: Effects of Inspiratory Muscle Training on Exercise Tolerance in Asthmatic Individuals

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 clinicallydiagnosed asthmatics underwent either 6 wks of inspiratory muscle training (IMT, n=7) consisting of 30 breaths twice-daily at 50% maximum inspiratory pressure (PImax), or sham-IMT (PLA, n=8) consisting of 60 breaths daily at 15% PImax. Time to the limit of exercise tolerance (Tlim) was assessed using constant power-output (70% peak power) cycle ergometery. Inspiratory muscle fatigue was determined by comparing the preto post-exercise reduction in PImax. 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 following the intervention. In contrast, in the IMT group, PImax increased by 28%, and Tlim by 16% (P<0.05). Dyspnea during exercise was also reduced significantly by 16% (P<0.05). The exercise induced fall in PImax was reduced from10% pre-IMT, to 6%, post-IMT (P<0.05), despite the longer Tlim. Conclusion: 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.