Inspiratory muscle function may be impaired in patients with COPD, which may lead to dyspnoea , impaired exercise tolerance  and hypercapnia . Several studies have therefore investigated the effects of inspiratory muscle training (IMT) on these parameters. IMT is generally started at a specific percentage of the maximal inspiratory pressure (PImax). The minimum load for achieving a real training effect is 30% of the PImax, which can be increased to 60-80%. Although most studies showed improved function of the inspiratory muscles after IMT [53-57], only a minority found a decrease in dyspnoea  or an improvement in exercise tolerance . The reasons for these disappointing results might be an inadequate training protocol or not including appropriate patients in the study . Gosselink and Decramer suggested that patients with ventilatory limitation might be ideal candidates . In contrast to this, both Larson et al.  and Sanchez Riera et al.  recently showed positive results of IMT on both dyspnoea and exercise performance in patients with COPD in whom a ventilatory limitation was not established.
In summary, there is at present no strong evidence that IMT is beneficial in all patients with COPD. It might be beneficial in a specific group of patients with a ventilatory limitation. To further clarify the role of IMT in a rehabilitation programme, more needs to be known about the optimal candidates and how these patients should be trained.
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