Exercise-induced improvements in the VO2peak of cardiac rehabilitation participants are well documented. However, optimal exercise intensity remains doubtful. This study aimed to identify the optimal exercise intensity and program length to improve VO2peak in patients with cardiovascular diseases (CVDs) following cardiac rehabilitation. Randomized controlled trials (RCTs) included a control group and at least one exercise group. RCTs assessed cardiorespiratory fitness (CRF) changes resulting from exercise interventions and reported exercise intensity, risk ratio, and confidence intervals (CIs). The primary outcome was CRF (VO2peak or VO2 at anaerobic threshold). Two hundred and twenty-one studies were found from the initial search (CENTRAL, MEDLINE, CINAHL and SPORTDiscus). Following inclusion criteria, 16 RCTs were considered. Meta-regression analyses revealed that VO2peak significantly increased in all intensity categories. Moderate-intensity interventions were associated with a moderate increase in relative VO2peak (SMD = 0.71 mL-kg-1-min-1; 95% CI = [0.27-1.15]; p = 0.001) with moderate heterogeneity (I2 = 45%). Moderate-to-vigorous-intensity and vigorous-intensity interventions were associated with a large increase in relative VO2peak (SMD = 1.84 mL-kg-1-min-1; 95% CI = [1.18-2.50], p < 0.001 and SMD = 1.80 mL-kg-1-min-1; 95% CI = [0.82-2.78] p = 0.001, respectively), and were also highly heterogeneous with I2 values of 91% and 95% (p < 0.001), respectively. Moderate-to-vigorous and vigorous-intensity interventions, conducted for 6-12 weeks, were more effective at improving CVD patients' CRF.
Keywords: cardiac rehabilitation; cardiorespiratory fitness; exercise therapy; heart diseases; high-intensity intermittent exercise.