Abstract
BACKGROUND: Several studies have highlighted the substantial role of the athlete's redox and inflammation status during the training process. However, many factors such as differences in testing protocols, assays, sample sizes, and fitness levels of the population are affecting findings and the understanding regarding how exercise affects related biomarkers in adolescent athletes. OBJECTIVES: To search redox homeostasis variables' and inflammatory mediators' responses in juvenile athletes following short- or long-term training periods and examine the effect size of those variations to training paradigms. METHODS: A PRISMA-compliant systematic review and meta-analysis were conducted. The entire content of PubMed (MEDLINE), Scopus, and Science Direct were systematically searched until December 2019. Studies with outcomes including (1) a group of adolescent athletes from any individual or team sport, (2) the assessment of redox and/or inflammatory markers after a short- (training session or performance testing) or longer training period, and (3) variables measured in blood were retained. The literature search initially identified 346 potentially relevant records, of which 36 studies met the inclusion criteria for the qualitative synthesis. From those articles, 27 were included in the quantitative analysis (meta-analysis) as their results could be converted into common units. RESULTS: Following a short training session or performance test, an extremely large increase in protein carbonyls (PC) (ES 4.164; 95% CI 1.716 to 6.613; Z = 3.333, p = 0.001), a large increase in thiobarbituric acid reactive substances (TBARS) (ES 1.317; 95% CI 0.522 to 2.112; Z = 3.247, p = 0.001), a large decrease in glutathione (GSH) (ES - 1.701; 95% CI - 2.698 to - 0.705; Z = - 3.347, p = 0.001), and a moderate increase of total antioxidant capacity (TAC) level (ES 1.057; 95% CI - 0.044 to 2.158; Z = 1.882, p = 0.060) were observed. Following more extended training periods, GSH showed moderate increases (ES 1.131; 95% CI 0.350 to 1.913; Z = 2.839, p = 0.005) while TBARS displayed a small decrease (ES 0.568; 95% CI - 0.062 to 1.197; Z = 1.768, p = 0.077). Regarding cytokines, a very large and large increase were observed in IL-6 (ES 2.291; 95% CI 1.082 to 3.501; Z = 3.713, p = 0.000) and IL-1 receptor antagonist (ra) (ES 1.599; 95% CI 0.347 to 2.851; Z = 2.503, p = 0.012), respectively, following short-duration training modalities in juvenile athletes. CONCLUSIONS: The results showed significant alterations in oxidative stress and cytokine levels after acute exercise, ranging from moderate to extremely large. In contrast, the variations after chronic exercise ranged from trivial to moderate. However, the observed publication bias and high heterogeneity in specific meta-analysis advocate the need for further exploration and consistency when we deal with the assessed variables to ascertain the implications of structured training regimes on measured variables in order to develop guidelines for training, nutritional advice, and wellbeing in young athletes. TRIAL REGISTRATION: PROSPERO CRD42020152105.