Abstract: Eight studies involving 262 participants were included in the review. Participants had stable asthma, with severity ranging from mild to severe. All studies were randomised trials, three studies had high withdrawal rates. Participants were between five to 18 years of age, and in seven studies swimming training varied from 30 to 90 minutes, two to three times a week, over six to 12 weeks. The programme in one study gave 30 minutes training six times per week. The comparison was usual care in seven studies and golf in one study. Chlorination status of swimming pool was unknown for four studies. Two studies used non-chlorinated pools, one study used an indoor chlorinated pool and one study used a chlorinated but well-ventilated pool. No statistically significant effects were seen in studies comparing swimming training with usual care or another physical activity for the primary outcomes; quality of life, asthma control, asthma exacerbations or use of corticosteroids for asthma. Swimming training had a clinically meaningful effect on exercise capacity compared with usual care, measured as maximal oxygen consumption during a maximum effort exercise test (VO2 max) (two studies, n = 32), with a mean increase of 9.67 mL/kg/min; 95% confidence interval (CI) 5.84 to 13.51. A difference of equivalent magnitude was found when other measures of exercise capacity were also pooled (four studies, n = 74), giving a standardised mean difference (SMD) 1.34; 95% CI 0.82 to 1.86. Swimming training was associated with small increases in resting lung function parameters of varying statistical significance; mean difference (MD) for FEV1 % predicted 8.07; 95% CI 3.59 to 12.54. In sensitivity analyses, by risk of attrition bias or use of imputed standard deviations, there were no important changes on effect sizes. Unknown chlorination status of pools limited subgroup analyses. Based on limited data, there were no adverse effects on asthma control or occurrence of exacerbations. This review indicates that swimming training is well-tolerated in children and adolescents with stable asthma, and increases lung function (moderate strength evidence) and cardio-pulmonary fitness (high strength evidence). There was no evidence that swimming training caused adverse effects on asthma control in young people 18 years and under with stable asthma of any severity. However whether swimming is better than other forms of physical activity cannot be determined from this review. Further adequately powered trials with longer follow-up periods are needed to better assess the long-term benefits of swimming.

Plain-language summary: We reviewed a total of eight studies involving 262 participants between the ages of five and 18 years with well-controlled asthma. They underwent swimming training varying from 30 to 90 minutes two to three times a week over six to 12 weeks in seven studies, and in one study training lasted 30 minutes six times per week. This review found that for swimming training compared to control (either usual care or another physical activity), there were improvements in resting lung function tests, but no effects were found on quality of life, control of asthma symptoms or asthma exacerbations. Physical fitness increased with swimming training compared with usual care. There were few reported adverse asthmatic events in swimming training participants during the programmes. The relatively small number of studies and participants limits this review’s ability to measure some outcomes that are of interest, particularly the impact on quality of life and  asthma exacerbations. In summary, swimming training is well-tolerated in children and adolescents with stable asthma, and increases physical fitness and lung function. However, whether swimming is better and/or safer than other forms of physical activity cannot be determined from this review. Further studies with longer follow-up periods may help us understand any long-term benefits of swimming.