Does chronic high-intensity endurance training have an effect on cardiovascular markers of active populations and athletes? Systematic review and meta-analysis

Objective The objective of this study was to ascertain the effects of high-intensity chronic endurance training on cardiovascular markers of active populations and athletes. Methods This review was conducted in accordance with the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. We used databases of PubMed, Science Direct, SPORTDiscus, Google Scholar and grey literatures with Mesh and free-text search as well as manual searches to identify relevant studies from June 2017 to September 2019. Weighted standardised mean differences and effect size of the intervention group versus the control group were calculated using a random effect model with 95% CI. Result There was significant improvement in high-density lipoprotein with weighted standardised mean difference and effect size=？1.06 (？1.83 to ？0.30), p=0.006. We have also observed a significant reduction in low-density lipoprotein and total cholesterol with weighted standardised mean difference and effect size=？0.97 (？1.58 to ？0.36), p=0.002, and = ？0.78 (？1.34 to ？0.22), p=0.007, respectively. There was a significant reduction in interleukin 6 (IL-6) using a fixed effect model with weighted standardised mean difference and effect size=？0.87 (？1.33 to ？0.40), p=0.0003 and C reactive protein (CRP) with weighted standardised mean differences and effect size=？0.41 (？0.73 to ？0.09), p=0.01. Conclusion Chronic high-intensity endurance training improves healthy lipid profiles (increase high-density lipoprotein, decreased low-density lipoprotein and total cholesterol). And decreased inflammatory markers (IL-6 and CRP) independent of age and sex and cannot be associated with an increased risk of developing cardiovascular disease. PROSPERO registration number CRD 42017081369