Effects of nine weeks L-Carnitine supplementation on exercise performance, anaerobic power, and exercise-induced oxidative stress in resistance-trained males

Abstract

[Purpose]Studies of L-carnitine in healthy athletic populations have yielded equivocal results. Further scientific-based knowledge is needed to clarify the ability of L-carnitine to improve exercise capacity and expedite the recovery process by reducing oxidative stress. This study aimed to examine the 9-week effects of L-carnitine supplementation on exercise performance, anaerobic capacity, and exercise-induced oxidative stress markers in resistance-trained males.[Methods]In a double-blind, randomized, and placebo-controlled treatment, 23 men (age, 25±2y; weight, 81.2±8.31 kg; body fat, 17.1±5.9%) ingested either a placebo (2 g/d, n=11) or L-carnitine (2 g/d, n=12) for 9 weeks in conjunction with resistance training. Primary outcome measurements were analyzed at baseline and at weeks 3, 6, and 9. Participants underwent a similar resistance training (4 d/w, upper/lower body split) for a 9-week period. Two-way ANOVA with repeated measures was used for statistical analysis.[Results]There were significant increases in bench press lifting volume at wk-6 (146 kg, 95% CI 21.1, 272) and wk-9 (245 kg, 95% CI 127, 362) with L-carnitine. A similar trend was observed for leg press. In the L-carnitine group, at wk-9, there were significant increases in mean power (63.4 W, 95% CI 32.0, 94.8) and peak power (239 W, 95% CI 86.6, 392), reduction in post-exercise blood lactate levels (-1.60 mmol/L, 95% CI -2.44, -0.75) and beneficial changes in total antioxidant capacity (0.18 mmol/L, 95% CI 0.07, 0.28).[Conclusion]L-carnitine supplementation enhances exercise performance while attenuating blood lactate and oxidative stress responses to resistance training.

The bright and the dark sides of L-carnitine supplementation: a systematic review

“…It has been assumed that a combination of LC supplementation with increased energy expenditure may positively affect body composition. However, either with aerobic [ 41 , 42 ] or resistance [ 43 ] training, LC supplementation has not achieved successful endpoint. Six weeks of endurance training (five times per week, 40 min on a bicycle ergometer at 60% maximal oxygen uptake) together with LC supplementation (4 g/day) does not induce a positive effect on fat metabolism in healthy male subjects (% body fat 17.9 ± 2.3 at the beginning of the study) [ 41 ].…”

“…In the recent study, LC supplementation 2 g/day has been applied in combination with a resistance training program (4 days/week) to healthy men (age range 18–40 y.o. ), for 9 weeks [ 43 ]. Body composition, determined by dual energy X-ray absorptiometry, indicated no significant effect in fat mass and fat-free mass due to supplementation.…”

“…Moreover, LC administration did not influence bench press results. The number of leg press repetitions and the leg press third set lifting volume increased in the LC group compared to the placebo group [ 43 ]. Different LC effect in the limbs may be associated with the higher rates of glycogenolysis during arm exercise at the same relative intensity as leg exercise [ 44 ].…”

“…This effect was accompanied by a significant reduction in released cytosolic proteins such as myoglobin and creatine kinase [ 50 , 52 , 53 ] as well as attenuation in plasma marker of oxidative stress - malondialdehyde [ 51 , 53 , 54 ]. Furthermore, 9 weeks of LC supplementation in conjunction with resistance training revealed a significant increase of circulating total antioxidant capacity and glutathione peroxidase activity and decrease in malondialdehyde concentration [ 43 ].…”

15N‐carnitine, a novel endogenous hyperpolarized MRI probe with long signal lifetime

“…Carnitine is a closely related quaternary nitrogen compound with much better safety profile than choline, having previously been administered intravenously to humans at gram doses without adverse effects 21 . There is current controversy over the use of carnitine supplementation in patients on dialysis, 22 diabetes, 23 and for improving exercise performance, 24 and there is little prior work on radiolabeled carnitine 25 . Carnitine has biochemical roles analogous to choline as a metabolic buffer for excess acetyl units as well as transport of long‐chain fatty acids into mitochondria for oxidation, through carnitine palmitoyltransferase I; therefore, its metabolism is especially important in tissues that rely heavily on fatty acids as a fuel of respiration, such as heart, liver, and kidneys 26,27 .…”