Introduction: Weakness of the respiratory muscles is a major cause for respiratory failure in Duchenne muscular dystrophy(DMD). Objective: To evaluate effects of inspiratory muscle training on respiratory muscle strength in patients with DMD. Method: Clinical trial with one group with five patients (DMD), aged 11.4±2.6 years, assessed by manovacuometry (MIP and MEP) and Peak Flow (PEF) in three stages: initial(baseline), five and ten session. Inspiratory muscle training, with 30% of MIP in linear load device (Threshold ®), five sets of 10 repetitions, totaling 10 sessions, three times a week. This work was approved by the ethics committee and the results were analyzed by Friedman test and Dunn test and calculation of effect size (r) of Cohen. Results: Mean initial, fifth and 10th session, respectively: MIP(cmH₂O) -64, -69.8 and -86.8; MEP(cmH₂O) 64, 67 and 73.6 and PEF(L/min) 210, 218 and 232. Friedmann test significant: MIP (p=0.006), MEP (p=0.003) and PEF (p=0.012). Dunn test: MIP: initial = 5sessions < 10sessions (p=0.527,p=0.040,p=0.007), a 29% improvement in initial sessions to 10th with effect size r=0.85 (major), explaining 72% of the total variance. MEP: Initial≤5sessions ≤10sessões (p=0.343,p=0.058,p=0.004), 25% improvement for initial to 10th session and effect size r=0.90 (large) explaining 81% of the total variance. PEF: Initial=5sessions<10sessions (p=0.752,p=0.027,p=0.011); improvement of 9% from initial to 10 sessions and effect size r=0.80 (major) explaining 64% of the total variance. Conclusion: Training proposed was effective in gaining respiratory strength in 10 sessions. Because the progression of DMD suggest permanent treatment aimed at maintaining and improving muscle strength.