Abstract: 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. There were 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. There is no conclusive evidence in this review to support or refute inspiratory muscle training for asthma. The evidence was limited by the small number of trials with few participants together with the risk of bias. More well conducted randomised controlled trials are needed. Future trials should investigate the following outcomes: lung function, exacerbation rate, asthma symptoms, hospital admissions, use of medications and days off work or school. Inspiratory muscle training should also be assessed in people with more severe asthma and conducted in children with asthma.

Plain-language summary: We found and included five studies in our review. Three studies were conducted by the same group of researchers in Israel (Weiner 2000; Weiner 2002; Weiner 2002a), one study (Sampaio 2002) was conducted in Brazil and one trial was conduced in the United Kingdom (McConnell 1998). A total of 113 adults with asthma (46 male and 67 female) were included. No study included children. The studies showed a significant improvement in inspiratory muscle strength (PImax). People with asthma who received IMT on average increased their inspiratory muscle strength, but it was not possible to state whether this improvement seen in inspiratory muscle strength translated into any clinical benefit. Results from one study showed no significant difference between the training group and the control group (no treatment or usual care) for expiratory muscle strength, lung function, sensation of dyspnoea (breathlessness) and use of reliever medication. There were no studies describing exacerbation events that required use of reliever medication or emergency department visits, inspiratory muscle endurance, hospital admissions and days off work or school. Given the insufficient evidence found in this review, we believe that there is a need for more well conducted studies in order to assess the efficacy of IMT in people with asthma, including children. There were substantial differences between the studies, including the training protocol, duration of training sessions (10 to 30 minutes) and duration of the intervention (over 3 to 25 weeks). The methodological quality of the studies included in this update was difficult to accurately ascertain. Study samples were small and the risk of bias was mostly unclear, due to inadequate reporting. Overall the quality of the evidence included in the review was very low. This summary was current to November 2012.