The characteristics and effects of exercise interventions on improving physical fitness in adults with asthma: a systematic review and meta-analysis

Introduction: Physical activity and fitness is beneficial for asthma-related outcomes and overall health. Experts are calling for exercise training to be embedded within asthma care and for the development of asthma-specific physical activity guidelines. This systematic review aimed to identify the characteristics and determine the effects of exercise interventions on improving physical fitness in adults with asthma. Methods: A systematic search was completed in MEDLINE, CINAHL, EMBASE and SportsDISCUS for peer-reviewed publications of empirical studies that investigated the effects of an exercise training intervention on performance-based measures of physical fitness outcome(s) in adults with asthma. Two reviewers independently screened studies for inclusion according to predetermined criteria and performed data extraction and quality assessment of included studies. Results: Thirty-nine articles were included, in which results for 33 unique studies were reported. Subjects (n=1,726) were aged (mean ± SD) 22±4 to 71 ± 11 years with mild-severe asthma. Most exercise programs used aerobic exercise (97%), alone (39%) or in combination with resistance, stretching and/or breathing exercises (58%). Resistance exercise featured in 39% of studies, stretching exercise in 36% and breathing exercise in 24%. The most common exercise program characteristics were supervised moderate-to-vigorous intensity aerobic exercise performed for 31-45 minutes three days/week. Meta-analyses revealed significant improvements in cardiorespiratory (VO2peak: MD 3.46mL/kg/min, 95% CI 2.55, 4.38, p<0.00001) and functional (6MWD: MD 56.7m, 95% CI 34.5, 78.9, p<0.00001) fitness in favour of experimental exercise training interventions. Findings regarding muscular fitness were not able to be pooled quantitatively, and qualitative synthesis was inconclusive. The effects of unsupervised exercise programs are also unclear and understudied. Discussion: Supervised exercise training elicits improvements in cardiorespiratory and functional fitness in adults with asthma. Exercise training may have important clinical implications in addressing the increased risk of cardiovascular disease mortality amongst adults with asthma, as these improvements have previously been associated with 9% reduction in the risk of cardiovascular disease morbidity and 8-12% reduction in the risk of all-cause mortality in healthy and comorbid adults. Improvements in functional fitness also exceed minimum clinically important differences for healthy and comorbid adults including those with respiratory conditions. These findings complement previous review findings regarding effectiveness of aerobic exercise for asthma-related outcomes and should be considered collectively in the formation of asthma-specific physical activity guidelines to ensure they confer benefits to both asthma-related and overall health-related physical fitness outcomes. Further research on resistance exercise, as well as unsupervised and telehealth exercise programs, is required in this population. Conflict of interest statement: My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract.