BACKGROUND: The early institution of inspiratory muscle training on hospitalised patients with no established respiratory deficits could prevent in-hospital adverse outcomes that are directly or indirectly associated to the loss of respiratory muscle mass inherent to a prolonged hospital stay. The objective of the clinical trial is to assess the impact of inspiratory muscle training on hospital inpatient complications. METHODS: This is a double-blind randomised controlled trial. Subjects in the intervention group underwent an inspiratory muscle training loaded with 50% maximum inspiratory pressure twice daily for 4 weeks from study enrolment. Patients were randomly assigned to an inspiratory muscle training group or a sham inspiratory muscle training group. All patients received conventional physiotherapy interventions. Baseline and post-intervention respiratory and peripheral muscle strength, functionality (performance of activities of daily living), length of hospital stay, and death were evaluated. Clinical outcomes were assessed until hospital discharge. This study was approved by the Institutional Hospital Ethics Committee (03/2014). RESULTS: Thirty-one patients assigned to the inspiratory muscle training group and 34 to the sham inspiratory muscle training group were analysed. Patients in the inspiratory muscle training group had a shorter mean length of hospital stay (35.3 ± 2.7 vs. 41.8 ± 3.5 days, p < 0.01) and a lower risk of endotracheal intubation (relative risk (RR) = 0.36; 95% confidence interval (CI) 0.27-0.97; p = 0.03) as well as muscle weakness (RR = 0.36; 95% CI 0.19-0.98; p = 0.02) and mortality (RR = 0.23; 95% CI 0.2-0.94; p = 0.04). The risk of adverse events did not differ significantly between groups. CONCLUSION: Inspiratory muscle training was a protective factor against endotracheal intubation, muscle weakness, and mortality. TRIAL REGISTRATION: ClinicalTrials.gov, ID: NCT02459444 . Registered on 19 May 2015.