Does exercise-induced apelin affect sarcopenia? A systematic review and meta-analysis

Purpose/objective There have been a number of studies on the role of the novel protein apelin, identified in 1998, in improving muscular function and structure in various human organs, as well as on how it is involved in pathological processes. The aim of this systematic review and meta-analysis was to determine the effect of exercise on serum apelin levels to provide up-to-date data for the development of an exercise intervention for older adults. Methods We searched for articles in PubMed, Ovid MEDLINE, and EMBASE from database inception to May 31, 2019. To conduct a meta-analysis of the primary outcome (serum apelin level), we analyzed intervention effect sizes of the differences between the exercise group and control groups for the primary outcome measure at post-treatment. The outcomes were analyzed using Hedge's statistic effect size (Zr) for weight mean difference (WMD) from various statistical results, including t, F, x(2), and r. A heterogeneity test was conducted using Higgin's I-2 statistic and Q statistics (p > 0.10) via a forest plot. A fixed-effect model was considered if Higgin's I-2 was less than 50%. If heterogeneity was high (I-2 > 50%), a random-effects model with a subgroup analysis or meta-regression was used. A meta-analysis using nine studies showed that exercise could increase serum apelin levels, which was beneficial for such metabolic diseases as diabetes. Results In the subgroup analysis, the 50-60-year-old group showed significant effects of exercise. However, the BMI (normal, overweight, and obesity) categories failed to show any difference in exercise-induced effect. Conclusion Further studies are needed to clarify in greater detail the effect of resistance exercise on apelin levels, including data on frequency, type, intensity, and time of aerobic exercise, to compare their effects on sarcopenia and cognitive disorders.