PURPOSE: This study examined the effects of inspiratory muscle training (IMT) with high-intensity inspiratory pressure loads on respiratory muscle performance and exertional dyspnea.
METHODS: This was a randomized single-blind clinical trial. Twenty-seven patients with chronic obstructive pulmonary disease (18 men, 9 women) with severe to very severe airflow obstruction and severely limited functional performance were assigned randomly to an IMT group (n = 12) or an educational control group (n = 15). The IMT group trained with a threshold loaded device for 30 minutes a day for 16 weeks using interval training techniques. Training was initiated with inspiratory pressure loads equal to 30% of maximal inspiratory pressure (PI max ) and increased as tolerated to 60% of PI max . Dependent variables were measured before and after 4 months of IMT: inspiratory muscle strength (PI max ), respiratory muscle endurance (discontinuous incremental threshold loading test [DC-ITL]), dyspnea (Chronic Respiratory Disease Questionnaire [CRQ]), and the Borg Category-Ratio Scale ratings of perceived breathing difficulty (RPBD) at equal loads during the DC-ITL.
RESULTS: In the IMT group, PI max increased from 64 ± 15 to 75 ± 17 cm H 2 O (P < .05), performance on the DC-ITL test increased from a maximal load of 37 ± 12 to 53 ± 13 cm H 2 O (P < .05), RPBD decreased from 5.5 ± 2.5 to 3.8 ± 2.6 for equal loads on the DC-ITL (P < .05) and the CRQ Dyspnea Scale improved from 18.1 ± 5.1 to 22.4 ± 5.2 (P < .05).
CONCLUSIONS: Inspiratory muscle training at high-intensity loads significantly improved inspiratory muscle strength, respiratory muscle endurance, and respiratory symptoms during daily activities and respiratory exertion.