Acute Effects of Training Loads on Muscle Damage Markers and Performance in Semi-elite and Elite Athletes: A Systematic Review and Meta-analysis

Abstract

The relationship between exercise-induced muscle damage (EIMD) indicators and acute training loads (TL) is yet to be reviewed extensively in semi-elite and elite athlete populations. The objectives of this systematic review and meta-analysis were threefold: (1) to evaluate studies of EIMD following the initial period of the preseason in semi-elite and elite athletes: (2) to examine acute physiological and performance responses across two periods of the season with similar TL; and (3) to examine acute physiological and performance responses to acute changes in TL during the season. The CINAHL, PubMed, Scopus, SPORTDiscus and Web of Science databases were systematically searched for studies that investigated: (1) semi-elite or elite athletes in team or individual sports following a periodised training programme; and (2) measured acute responses to training. Studies were excluded if: (1) conducted in animals; (2) non-English language; or (3) a conference abstract, review or case report. The Kmet Quality Scoring of Quantitative Studies tool was used for study appraisal. Data were quantitatively analysed by generating forest plots to report test statistics for statistical significance and inter-trial heterogeneity. Of the included studies (n\u2009=\u200932), athletes experienced greater creatine kinase (CK) concentrations (Z\u2009=\u20094.99, p\u2009<\u20090.00001, I2\u2009=\u200974%), inflammatory factors and other indirect measures of muscle damage in the initial phase of the preseason period compared to the off-season; there were no changes in CK (Z\u2009=\u20091.43, p\u2009=\u20090.15, I2\u2009=\u200974%) across two time points of similar TL; and there were concurrent increases in CK with increases in TL (Z\u2009=\u20094.26, p\u2009<\u20090.0001, I2\u2009=\u200936%) and vice versa (Z\u2009=\u20094.33, p\u2009<\u20090.0001, I2\u2009=\u200979%).The qualitative analysis identified that the response of inflammatory factors and other indirect measures of muscle damage to changes in load were inconclusive. This review included varying age, sex, sports and competition levels. The group level meta-analysis failed to identify within-athlete or position-specific differences across time. Blood biomarkers of EIMD may not differ across periods of similar TL, however can be considered a sensitive monitoring tool for assessing responses following acute TL changes in semi-elite and elite athletes.