RESUMO
Objectives: The aim of this meta-analysis was to determine the effects of respiratory muscle training (RMT) on functional ability, pain-related outcomes, and respiratory function in individuals with sub-acute and chronic low back pain (LBP). Methods: The study selection was as follows: (participants) adult individuals with >4 weeks of LBP; (intervention) RMT; (comparison) any comparison RMT (inspiratory or expiratory or mixed) versus control; (outcomes) postural control, lumbar disability, pain-related outcomes, pain-related fear-avoidance beliefs, respiratory muscle function, and pulmonary function; and (study design) randomized controlled trials. Results: 11 studies were included in the meta-analysis showing that RMT produces a statistically significant increase in postural control (mean difference (MD) = 21.71 [12.22; 31.21]; decrease in lumbar disability (standardized mean difference (SMD) = 0.55 [0.001; 1.09]); decrease in lumbar pain intensity (SMD = 0.77 [0.15; 1.38]; increase in expiratory muscle strength (MD = 8.05 [5.34; 10.76]); and increase in forced vital capacity (FVC) (MD = 0.30 [0.03; 0.58]) compared with a control group. However, RMT does not produce an increase in inspiratory muscle strength (MD = 18.36 [-1.61; 38.34]) and in forced expiratory volume at the first second (FEV1) (MD = 0.36 [-0.02; 0.75]; and in the FEV1/FVC ratio (MD = 1.55 [-5.87; 8.96]) compared with the control group. Conclusions: RMT could improve expiratory muscle strength and FVC, with a moderate quality of evidence, whereas a low quality of evidence suggests that RMT could improve postural control, lumbar disability, and pain intensity in individuals with sub-acute and chronic LBP. However, more studies of high methodological quality are needed to strengthen the results of this meta-analysis.