Effect of an acute exercise bout on immediate post-exercise irisin concentration in adults: A meta-analysis.

Irisin is a recently discovered myokine that increases adipocyte metabolism, induces further "browning" of white adipose tissue, and enhances glucose metabolism. No study has ever determined how an acute bout of exercise impacts immediate post-exercise irisin concentration using a meta-analytic approach. The purpose of this study is to determine the impact of an acute bout of exercise on the magnitude of post-exercise irisin concentration in adults using meta-analytic procedures. Searches were performed on PubMed, EMBASE, CINAHL, PEDro, SCOPUS, and SPORTDiscus databases. Effect summaries were obtained using random-effects models. Random-effects single and multiple meta-regressions were performed to determine relationships between, and potential confounding effects of, variables of interest. Ten articles were retained for the final meta-analysis, producing 21 study estimates. An acute bout of exercise was accompanied by a post-exercise average increase in irisin concentration of 15.0 (95% CI: 10.8%-19.3%). There was no significant relationship between post-exercise irisin concentration and age, intensity of aerobic exercise, or type of exercise training session (resistance vs aerobic training). Fitness level and body mass index were identified as significant predictive variables for post-exercise irisin concentration. However, a multiple meta-regression model identified fitness level as the single best predictor, with being fit (21.1%±2.2%) associated with a nearly twofold increase in post-exercise irisin concentration, compared with being unfit (11.8%±2.1%). Immediately following an acute bout of exercise, irisin concentration increases substantially in adults, with fitness level as an important modifier for the effect.