Effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors: A systematic review and meta-analysis

Background Knowledge of the optimal protocol and safety of particularly high-intensity exercise applied to individuals with stroke is lacking. Objective This systematic review and meta-analysis aimed to investigate the effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors. Methods We performed a systematic electronic search for articles in MedLine via PubMed, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials, CINAHL, and SPORTSDiscus up to April 1, 2019. Peak oxygen consumption (VO 2 peak), 6-min walk test (6MWT), fastest 10-m walk test (10MWT), and adverse events were assessed. The standardized mean difference (SMD), weighted mean difference (WMD), and odds ratios (ORs) were used to compute the effect size, and subgroup analysis was conducted to test the consistency of results as well as sensitivity analysis to assess the robustness of the results. The quality of evidence was assessed with the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. Results We included 17 studies (PEDro score ≥ 4) in the meta-analysis. Post-intervention, high-intensity exercise had a significant effect on peak oxygen uptake (VO 2 peak; SMD = 0.56, P < 0.01, I 2 = 8%; WMD = 2.53 mL/kg/min; high quality of evidence) and 6MWT (SMD = 0.26, P < 0.01, I 2 = 40%; WMD = 17.08 m; moderate quality of evidence) but not fastest 10MWT (SMD = 0.33, P = 0.27, I 2 = 77%; WMD = 0.05 m/s; low quality of evidence). Subgroup analysis showed better effects of higher-intensity treadmill training (≥ 70% heart rate reserve/VO 2 peak) for a longer duration (≥ 12 weeks) on VO 2 peak and 6MWT in sub-acute or chronic stroke survivors. The high-intensity exercise and control groups did not differ in adverse events including falls [odds ratio (OR) 1.40, P = 0.35, I 2 = 11%; low quality of evidence], pain (OR 3.34, P = 0.09, I 2 = 0%; moderate quality of evidence), or skin injuries (OR 1.08, P = 0.90, I 2 = 0%; low quality of evidence). Conclusions Our meta-analysis suggests that high-intensity exercise is beneficial for cardiorespiratory fitness in stroke survivors and might be safe as a novel intervention in cardiopulmonary rehabilitation after stroke.