Does exercising at a certain time-of-day affect athletes skeletal muscle damage markers? A systematic review and meta-analysis

Abstract

Abstract The objective of the study was to examine time of day effects of exercise on athletes’ skeletal muscle damage markers. The skeletal muscle damage marker enzymes like creatine kinase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase are the markers of the functional status of muscle tissue and vary widely with pathological and physiological conditions. 2212 potential citations were identified through PubMed, MEDLINE, SPORTDiscus, EMBASE and Google Scholar searches. Based on the eligibility criteria, 10 studies were included for analysis. Heterogeneity test (I2), Effect Size (ES) and Standardized Mean Differences (Std. MD) for time of day results were calculated at 95% CI and 5% alpha-level for each study. The protocol is registered in PROSPERO with registration number (PROSPERO 2018: CRD42018112116). Using a random effect model, the overall pooled time of day effect of exercise were, SMD = −1.82 (95%CI, -2.69, -0.95;P < 0.001) and (I2 = 76%) for lactate dehydrogenase, SMD = −1.44 (95%CI, -2.43, -0.46;P < 0.004) and (I2 = 74%) for creatine kinase, SMD = −1.89 (95%CI, -2.49, -1.30;P < 0.001) and (I2 = 22%) for aspartate aminotransferase, SMD = −0.73 (95%CI, -1.39, -0.07;P < 0.03) and (I2 = 56%) for alanine aminotransferase, SMD = −1.46 (95%CI, -1.94, -0.98;P < 0.001) and (I2 = 41%) for white blood cells (WBC). Our study partly confirms the diurnal variations of skeletal muscle damage markers and recommends conducting further meta-analysis to investigate the concomitant effect of exercise and time-of-day variations in relation to hormonal, core temperature and oxidative responses. The results obtained from our study may help athletes, active individuals, team physicians and coaches to consider these markers and protect the physicians from misinterpreting abnormal values when evaluating the training level of their athletes.