Effects of L-carnitine supplementation on markers of exercise-induced muscle damage in healthy adults: A systematic review and meta-analysis of randomized controlled trials

L-carnitine supplementation is purported to attenuate exercise-induced muscle damage, however, individual studies revealed mixed results. Thus, we performed a systematic review and meta-analysis of randomized controlled trials to determine the pooled effects of L -carnitine supplementation on muscle soreness and indirect circulating biochemical markers of muscle damage (myoglobin, creatine kinase (CK), and lactate dehydrogenase (LDH)) in healthy adults. Searches were performed on PubMed, Scopus, and Web of Science for randomized controlled trials (RCTs) examining L -carnitine supplementation on muscle damage or related biomarkers. Meta-analyses were done to calculate the weighted mean difference (WMD) when sufficient data was available. A total of 14 RCTs, including 284 participants, were included. L -carnitine supplementation doses varied from 1 to 3 g/d, from a single dose administration to an 8-week chronic regimen. Pooled effects revealed that L -carnitine reduced muscle soreness at 24 h [WMD= -6.39, p = 0.001] and 48 h after exercise [WMD= -1.53, p = 0.03]. Myoglobin was reduced immediately [WMD= -11.55 ng/mL, p = 0.04] and 30–60 min after exercise [WMD= -41.09 ng/mL, p = 0.001], but not 24 h after exercise [WMD= -22.85 ng/mL, p = 0.07]. CK was reduced 2 h [WMD= -26.72 IU/L, p = 0.02] and 24 h after exercise [WMD= -48.72 IU/L, p = 0.006], with no significant changes immediately after exercise [WMD= -32.76 IU/L, p = 0.38]. A non-significant decrease in LDH [WMD= -25.66 IU/L, p = 0.14] was observed immediately after exercise. In conclusion, L -carnitine supplementation may reduce muscle soreness, myoglobin and CK post-exercise, in some instances. Further research is warranted to determine the effects of L -carnitine on exercise performance.