Accumulating evidence of previous experimental studies indicated that L-Carnitine positively ameliorates muscle damage. However, findings from trials vary substantially across studies. Therefore, current meta-analysis aimed to examine the effects of L-Carnitine supplementation on exercise-induced muscle damage. An electronic search of the online literature databases (Medline (PubMed), Scopus and Google Scholar) was performed up to November 2018. Either a fixed-effects model or a random-effects model (Diasorin-Liard) was used in order to estimate the effects size. Cochran's Q test and I2 tests were used to assess the heterogeneity among the studies. Funnel plot and Egger's regression test were also employed in order to assess the publication bias. Of 604 studies, seven eligible randomized controlled trials (RCTs) were included in this meta-analysis. Pooled data from seven studies showed that L-Carnitine resulted in significant improvements in muscle soreness (MS) at the five follow-up time points (0, 24, 48, 72 and 96 hours (h)) compared to placebo. Also, pooled data indicated that L-Carnitine significantly reduced creatine kinase (CK), myoglobin (Mb), and lactate dehydrogenase (LDH) levels at one follow-up period (24 h). However, no effects have been observed beyond this period. Our outcomes indicate that L-Carnitine supplementation improves delayed-onset muscle soreness (DOMS) and markers of muscle damage. Further research is needed to clarify impacts of L-Carnitine on DOMS after different types of mechanical or chemical damages.Key teaching pointsThe effect of L-Carnitine supplementation on exercise-induced muscle damage has come under scrutiny over many years.This systematic review and meta-analyses study investigated the effects of L-Carnitine supplementation on exercise-induced muscle damage.Overall, summary results indicate that L-Carnitine supplementation improves muscle soreness and markers of muscle damage (CK, LDH, and Mb).Overall, L-carnitine supplementation ameliorated muscle damage only in resistance training groups and untrained population.
Keywords: L-carnitine; Muscle soreness; meta-analysis; muscle damage; supplementation.