Six controlled studies (n=128) were included in the review.
The methodological quality score assigned to the included studies ranged from 15 to 29 (median 23). The main issues included lack of adequate description of the randomisation procedure, lack of similarity between the cointervention with the experimental intervention, and the absence of double-blinding.
Five studies examined respiratory muscle strength. No statistically significant between-group differences in inspiratory mouth pressure were found, based on two studies comparing inspiratory muscle training with a control group. Of two studies examining expiratory mouth pressure, one found a significant improvement in favour of the intervention group (expiratory muscle training) compared with no training. One study found an increase in pectoral strength from baseline in the intervention group, but no change in the control group; no between-group comparison was made.
Two studies provided inspiratory muscle endurance training. Both studies found that endurance improved from baseline in the intervention group following RMT, but no significant between-group differences were found.
Five studies examined the effect of RMT on vital capacity: one found a significant improvement with expiratory muscle training compared with a control group. Three studies examined the effect of RMT on residual volume: two studies providing inspirational muscle training reported no changes in residual volume, while one study providing expiratory muscle training found a significant decrease in residual volume from baseline with RMT; however, no between-group comparisons were performed.
Respiratory complications, quality of life and exercise performance.
One study examined the effect of RMT on dyspnoea: a significant difference in favour of resistive inspiratory muscle training was found compared with no training. Another study looking at maximal sustained inspirations compared with no training reported some improvement in breathing during the exercise period; however, two patients were also reported to have increased spasms and sputum production. One study examined the effect of RMT on exercise performance: peak oxygen consumption during incremental maximal arm cranking exercise significantly improved after RMT.