We included five studies involving 113 adults. Participants in four studies had mild to moderate asthma and the fifth study included
participants independent of their asthma severity.Therewere substantial differences between the studies, including the training protocol,
duration of training sessions (10 to 30 minutes) and duration of the intervention (3 to 25 weeks). Three clinical trials were produced
by the same research group. Risk of bias in the included studies was difficult to ascertain accurately due to poor reporting of methods.
The included studies showed a statistically significant increase in inspiratory muscle strength, measured by maximal inspiratory pressure
(PImax) (mean difference (MD) 13.34 cmH2O, 95% CI 4.70 to 21.98, 4 studies, 84 participants, low quality evidence). Our other
primary outcome, exacerbations requiring a course of oral or inhaled corticosteroids or emergency department visits, was not reported.
For the secondary outcomes, results from one trial showed no statistically significant difference between the inspiratory muscle training
group and the control group for maximal expiratory pressure, peak expiratory flow rate, forced expiratory volume in one second, forced
vital capacity, sensation of dyspnoea and use of beta2-agonist. There were no studies describing inspiratory muscle endurance, hospital
admissions or days off work or school.