Investigation of the effect of L-Carnitine supplements in athletes on muscle damage and delayed onset muscle pain (DOMS) after high intensity interval training

During the preparatory phase of a sports season, physiological insufficiency frequently leads to early onset of fatigue and a prolonged recovery/regeneration period. This process adversely affects performance for both athletes and coaches. As fatigue increases following high-intensity and high-volume exercise, structural damage occurs in the sarcomeres of the actively engaged muscles. This sequence results in exercise induced muscle damage, leading to a temporary decline in both training efficiency and the athlete's developmental progress. On the other hand, L-Carnitine supplementation has been reported to elicit beneficial effects on exercise-induced muscle damage and delayed onset muscle soreness (GKA) in both healthy individuals and athletes. Purpose: The aim of this study was to investigate the effects of L-Carnitine supplementation on exercise-induced muscle damage and delayed onset muscle soreness (GKA) in trained athletes following high-intensity interval training (HIIT). Methods: Twenty-five male athletes participated in a double-blind, randomized, placebo-controlled trial. Participants were randomly assigned to receive either 3 g/day of L-Carnitine or a placebo for 21 days. A Wingate-based high-intensity interval exercise protocol was applied before and after the supplementation period. Blood samples were collected before the supplementation, before the exercise, and at 2, 24, and 72 hours post-exercise to assess muscle damage markers (CK and LDH). Additionally, fingertip blood lactate levels were measured at 1, 3, 5, 7 and 9 minutes post-exercise. Results: Plasma total carnitine concentrations were significantly higher at all time points in the L-Carnitine group compared to the placebo group (p<0.05). No significant differences were observed in peak power output between pre- and post-tests in either group (p>0.05). CK and LDH levels showed similar increases across both groups (p>0.05). GKA ratings at 2 and 24 hours post-exercise were significantly higher in the L-Carnitine group (p<0.05), whereas no differences were found at 48 and 72 hours (p>0.05). Blood lactate responses were also similar between groups (p>0.05). Conclusion: Based on the data obtained from the study, although a 21-day L-carnitine supplementation resulted in an increase in plasma total carnitine concentration in athletes, it did not provide an ergogenic benefit compared to the control group in terms of power output during high-intensity exercise, delay of fatigue, body composition, post-exercise recovery, resting heart rate, or in the primary focus of our study—delayed onset muscle soreness and exercise-induced muscle damage. Keywords: Athlete Nutrition, Delayed Onset Muscle Soreness, Ergogenic Aid, High Intensity Interval Training, L-Carnitine, Muscle Damage