L-carnitine and Weight Loss 5. L-carnitine and Recovery from Strenuous Exercise 6. Effects of L-carnitine on Athletic Performance and Recommended Dosage 7. Bioavailability of L-carnitine in Athletes 8.

Introduction Carnitine Lhydroxytrimethylamminobutanoate is an endogenous compound that can be synthesized in the liver and kidney from the essential amino acids lysine and methionine or ingested through diet [8, 10, 27, 57]. L-carnitine plays a critical role in energy production and in fat metabolism through its function as a transporter of long-chain fatty acids into mitochondria for β-oxidation [17].

In cells, it helps transport fatty acids into the mitochondria, where they can be burned for energy. Primary sources of dietary carnitine are red meat and dairy products. L-carnitine often receives patients with regular hemodialysis, with metabolic disorders and in pregnancy [33, 42].

However, L-carnitine plays a crucial role in exercise and among athletes. A few studies demonstrated the effects of L-carnitine in endurance athletes.

Endurance athletes use this supplementation to increase the oxidation of fat during exercise and spare muscle glycogen [25]. One of the main functions of performance enhancing drugs is to increase the amount of red blood cells. It is often times overlooked, be-cause of the obvious anabolic effects of performance enhancing drugs.

By increasing the oxygen carrying capability of the blood, it helps give the body an additional boost especially in stressful situations. Acetyl-L-Carnitine Acetyl-L-carnitine, or ALCAR, is L-carnitine to which an acetyl group -COCH3 has been added, is thought to be the most bioavailable form of L-carnitine.

Acetyl-L-Carnitine is an amino acid the body uses to turn fat into energy. It may also be used to treat neurological conditions such as Alzheimer's disease. Also, is a popular endurance supplement that plays a key role in energy production. There are many benefits of this supplementation for endurance athletes, but the most important are that improve exercise performance, improve recovery after following exercise, reduce muscle damage and soreness, increase ATP levels and improve antioxidant status.

Propionyl-L-Carnitine Also, is formed principally during amino acid catabolism [44]. The main role of PLC is that helps the body to produce energy. Furthermore, PLC is known to decrease lipid peroxidation or the process wherein lipid membranes are attacked by free radicals, causing cellular damage [3, 34].

Also helps increase the production of nitric oxide, which promotes blood circulation and regulates blood pressure [2]. For endurance athletes, cellular damage could mean longer recovery times and be more prone to muscular injuries in training sessions. Also, is formed principally during amino acid catabolism.

L-Carnitine L-Tartrate L-carnitine L-tartate is the one of the most common forms found in sports supplements, due to its rapid absorption rate [13, 49, 45]. This supplement is found to decrease muscle damage during recovery from resistance exercises [23].

Several studies found that 3 weeks supplementation with L-carnitine L-tartate reduces muscle damage produced by an acute bout of high intensity resistance exercise [28, 50]. L-Carnitine Deficiency L-carnitine deficiency is caused by a deficiency in the plasma membrane carnitine transporter with urinary carnitine wasting causing systemic carnitine depletion.

Intracellular carnitine deficiency impairs the entry of long-chain fatty acids into the mitochondrial matrix [16].

Systemic primary carnitine deficiency is characterized by episodes of hypoketonic, hypoglykemia, hepatomegaly, elevated transaminases, and hyperammonemia in infants; skeletal myopathy, elevated creatine kinase CK , and cardiomyopathy in childhood; or fatigability in adulthood [14].

The diagnosis is established by demonstration of low plasma free carnitine concentration In a Japanese study [29], primary systemic carnitine deficiency was estimated to occur in 1 per 40, births.

Wilcken et al. The frequency of this condition in adults is not known. However, in the United Kingdom, a previous report identified 4 affected mothers in 62, infants screened, with a frequency of , No studies have estimated the incidence of primary carnitine deficiency in the United States and in Europe, however is estimated to occur in approximately 1 in 20,, individuals based on newborn screening data from various states including Missouri, Texas, and California.

L-carnitine and Weight Loss Three studies found dietary carnitine intake to be important, and evidence suggests it may promote weight loss by increasing calorie expenditure [24, 46, 47].

The study of Stephens et al. A systematic review and meta-analysis of randomized control trials testing the effects of L-carnitine on weight loss [38].

In this meta-analysis were included nine studies and the participants supplemented with L-carnitine for at least one month.

The results from meta-analysis suggested that supplementing with L-carnitine led to a 1. L-carnitine supplementation led to significant weight loss in diabetic and non-diabetic individuals, as well as obese and nor-mal-weight people.

Additionally, the meta-analysis showed that the weight loss effects of L-carnitine are strongest in the beginning but decrease over time. However, the relevance of these findings is unclear because the included studies varied widely in their design.

In summary, this me-ta-analysis of randomized controlled trials suggests that supplementing with L-carnitine for more than a month may promote modest weight loss. L-carnitine and Recovery from Strenuous Exercise Found only two studies in distance runners that referred on the effects of L-Carnitine in recovery after high intensity training Table 1.

In a study by Colombani et al. Moreover, the study of Stuessi et al. Twelve subjects received either 2 g L-carnitine. Two hours after administration, the subjects performed a constant-load exercise test cycling at their individual anaerobic threshold to exhaustion.

They found that 2 g of L-carnitine taken 2 h before a first of two constant-load exercise tests had no influence on the second tests performed 3 h after the first test.

Also, one study used active healthy men. More especially, in a study by Parandak et al. Compared to the control group, those who took L-carnitine were found to have lower levels of certain markers that indicate muscle damage.

Table 1. Initially, in a study by Giamberardino et al. In a separate set of experiments carried out 8 months later, the possible effects of training on pain parameters and creatine kinase levels were also investigated in the same subjects.

It is concluded that L-carnitine has a protective effect against pain and damage from eccentric effort. Two papers from the same lab [22, 45] were also used in untrained male and female. After 3 weeks of L-carnitine supplementation loading, each participant then performed an acute resistance exercise.

They found that L-carnitine supplementation can reduce chemical damage and muscle soreness after physical exercise. On the contrary, there are some studies that referred in resistance trained subjects Table 1. Two studies from the same lab [28, 50] investigated the effects of L-carnitine supplementation on recovery after resistance exercise.

Blood was also sampled before and after a squat protocol 5 sets, 15—20 repetitions. The results demonstrate that L-carnitine supplementation is effective in assisting recovery from high-repetition squat exercise.

Effects of L-carnitine on Athletic Performance and Recommended Dosage Some athletes take L-carnitine to improve performance. Table 2 Table 2. Some studies found that this supplementation improve athletic performance.

More specifically, Gorostiaga et al. Also, in the study of Arenas et al. They found improvement in VO 2 max after L-carnitine administration. Table 2 On the other hand, some studies have seen not improve of performance in distance runners.

The study of Marconi et al. They suggested that this improvement is probably affected by variables, other than L-carnitine loading, of a physiological e.

Also, Colombani et al. Seven male subjects were given supplements of 2 g L-carnitine 2 h before the start of a marathon run and again after 20 km of the run. They found that acute administration of L-carnitine did not improve the physical performance of the endurance athletes during the run and did not alter their recovery.

In the study of Greig et al. The results of treatment with L-carnitine demonstrated no significant changes in VO 2 max or in maximum heart rate. Furthermore, in the study of Wachter et al. They found that supplementation of L-carnitine is not associated with a significant increase.

Even high doses have not resulted in improved carnitine concentrations in muscle and no change in function. The only way to increase carnitine in muscle is very prolonged carnitine supplementation in conjunction with a very high carbohydrate load or any other feeding that produces high insulin levels.

Whether this is a practical strategy is questionable. Stephens FB, Constantin-Teodosiu D, Laithwaite D, Simpson EJ, Greenhaff PL. An acute increase in skeletal muscle carnitine content alters fuel metabolism in resting human skeletal muscle.

J Clin Endocrinol Metab. doi: Epub Sep PMID: Stephens FB, Evans CE, Constantin-Teodosiu D, Greenhaff PL. Carbohydrate ingestion augments L-carnitine retention in humans.

J Appl Physiol Epub Nov Stephens FB, Wall BT, Marimuthu K, Shannon CE, Constantin-Teodosiu D, Macdonald IA, Greenhaff PL. Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans.

J Physiol. Epub Jul 1. PMID: ; PMCID: PMC Barnett C, Costill DL, Vukovich MD, Cole KJ, Goodpaster BH, Trappe SW, Fink WJ. Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling. Int J Sport Nutr. Vukovich MD, Costill DL, Fink WJ.

Carnitine supplementation: effect on muscle carnitine and glycogen content during exercise. Med Sci Sports Exerc. Wall BT, Stephens FB, Constantin-Teodosiu D, Marimuthu K, Macdonald IA, Greenhaff PL.

Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. Epub Jan 4. Are extreme glycogen loading protocols necessary? Does collagen strengthen connective tissue in muscle? Is fructose bad for health?

The optimal ratio of carbohydrates. Does dehydration reduce performance? Iron infusion or injection for athletes. If you want to find out the best types of protein, optimal amounts, or timing. Click here. Want to know more about nutrition for running. Greig C, Finch KM, Jones DA, Cooper M, Sargeant AJ, Forte CA The effect of oral supplementation with L-carnitine on maximum and submaximum exercise capacity.

Eur J Appl Physiol — Hultman E, Cederblad G, Harper P Carnitine administration as a tool to modify metabolism during exercise letter. Eur J Appl Physiol Marconi C, Sassi G, Carpinelli A, Ceretelli P Effects of L-carnitine loading on the aerobic and anaerobic performance of endurance athletes.

Eur J Appl Physiol —5. Maurer C Les effets de l'adjonction orale de L-carnitine sur l'exercise intense et prolongé chez le sportif. Thesis, Université Claude-Bernard, Lyon I. McGarry JD, Robles-Valdes C, Foster DW Role of carnitine in hepatic ketogenesis. Proc Nat Acad Sci USA —8.

Newsholme EA, Leech AR Biochemistry for the medical sciences. J Wiley Chicester, p Oyono-Enguelle S, Freund H, Ott C, Gartner M, Heitz A, Marbach J, Maccari F, Frey A, Bigot H, Bach AC Prolonged submaximal exercise and L-carnitine in humans.

Ruff LJ, Miller LG, Brass EP Effect of exogenous carnitine on carnitine homeostasis in the rat. Biochim Biophys Acta —9. Soop M, Bjorkman O, Cederblad G, Hagenfeldt L, Wahren J Influence of carnitine supplementation on muscle substrate and carnitine metabolism during exercise.

J Appl Physiol —9. Trappe SW, Costill DL, Goodpaster B, Vukovich MD, Fink WJ The effects of L-carnitine supplementation on performance during interval swimming. Int J Sports Med —5. Uhlenbruck G, van Mil A Immunlogische Experimente mit L-Carntin: neue, sportmedizinisch relevante Aspekte?

Dtsch Z Sportmed 43 [Suppl] 1—8. Wagenmakers AJM L-carnitine supplementation and performance in man. In: Brouns F ed Advances in nutrition and top sport. Med Sport Sci Eur J Appl Physiol —6.

Download references. INW Gruppe Ernährungsbiologie, ETH Zentrum, CH, Zürich, Switzerland. INW Gruppe Physiologie und Tierhaltung, ETH Zentrum, CH, Zürich, Switzerland. Klinische Pharmakologie und Toxikologie, Departement für Innere Medizin, Universitätspital, CH, Zürich, Switzerland. Klinik W.

Schulthess, Neumünsterallee 3, CH, Zürich, Switzerland. You can also search for this author in PubMed Google Scholar. Reprints and permissions. Colombani, P. et al. Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study.

Europ J Appl Physiol 73 , —

In a nutshell, yes, yes and yes. It is safe, it is legal at most available oral doses and some fairly solid science says it can boost performance if taken the right way over the right period of time.

On a cellular level, these benefits are achieved because L-carnitine helps fatty acids get into cellular mitochondria where it is converted to energy, while moving metabolic waste away.

Powerful stuff, really. The lead researcher of that and many other L-carnitine based studies, the eminent professor Paul Greenhaff told The Draft of his research between evacuating his University of Nottingham Medical School office amid the COVID lockdown.

Professor Greenhaff emphasises the importance of consuming L-carnitine with insulin-boosting carbohydrates to achieve efficacious L-carnitine levels in the muscle where it matters most.

New customer? Create your account. Lost password? Recover password. Remembered your password? Back to login. Already have an account? Login here. Optimizing your performance through nutrition and supplementation is how you set yourself apart from the competition.

L-carnitine is a proven ergogenic aid and has an arsenal of evidence that shows it can promote fat loss, optimize workout recovery, and enhance endurance in athletes. Often thought of as an amino acid, l-carnitine is actually a vitamin like, and amino-acid like compound that is formed from the amino acids lysine and methionine.

Carnitine is related to the B-Vitamins and was referred to as vitamin BT when it was first discovered. The main function of l-carnitine is the transport of long chain fatty acids, into the mitochondrial matrix for oxidation and conversion to energy. L-carnitine also plays an imperative role in the regulation of metabolic signaling pathways involved in muscle protein balance, proteolysis and muscle protein synthesis.

L-carnitine shuttles long-chain fatty acids inside the mitochondria by forming a long chain acetylcarnitine ester. The complex is then transported into the mitochondrial matrix by carnitine palmitoyltransferase I CPT I and carnitine palmitoyltransferase II CPT II.

The fatty acids are then broken down through the process of β-oxidation to deliver the 2-carbon molecules to the Krebs cycle, leading to the generation of energy under the form of adenosine triphosphate ATP. In addition, by binding an acetyl group, l-carnitine can maintain the levels of Acetyl-CoA and coenzyme A, playing its buffering role.

Research suggests that L-carnitine has several beneficial effects on physical performance, demonstrating an increase in maximal oxygen uptake, and higher power output.

Studies have also shown that L-carnitine supplementation may improve exercise recovery, by alleviating muscle injury, and reducing markers of cellular damage. Studies in older adults have shown positive impacts on physical and mental fatigue and that L-carnitine can lead to an increase in muscle mass and decrease in body weight [1].

L-Carnitine assists in transporting and oxidizing long chain fatty acids for muscle fuel or energy. Studies show that increasing total carnitine content could alter muscle fuel metabolism in two different ways during training.

In addition to fat oxidation, L-carnitine also enhances insulin response, balancing glycogen levels by reducing carbohydrate use, consistent with an increase in body fat utilization.

A systematic review that investigated the beneficial effects of L-Carnitine supplementation for weight management in overweight and obese adults found that L-Carnitine significantly reduced weight, BMI , and fat mass [2].

Workout recovery is crucial to overall athletic performance. Severe soreness can lead to potential injury due to overuse and increased muscular pain, interfering with your training schedule.

If you can optimize recovery through nutrition and supplement protocols, you can effectively increase training volume and performance.

Research shows that l-carnitine has several different mechanisms which can reduce muscle soreness and post workout muscular pain. The association between L-carnitine and the regulation of metabolic pathways involved in muscle protein balance may help protect muscles against atrophy or muscle mass breakdown, which can reduce soreness.

Evidence suggests that l-carnitine supplementation attenuates the use of amino acids as an energy source, making them more bioavailable for protein synthesis. If there are more amino acids freely available, they can further assist in muscle growth and muscle repair [3].

Studies also suggest that l-carnitine may improve blood flow therefore reducing muscle catabolism, and markers of metabolic stress. RELATED ARTICLE What Are Amino Acids? Athletes were given a glass of fruit juice 1 hour before applying L-carnitine with the double-blind method.

Then, 12 participants were given 3 g of L-carnitine LK-3 and the remaining 14 were given 4 g LK Athletes began the exercise test at a running speed of 8 km·h and then continued at 10 km·h. The speed was increased 1 km·h every 3 minutes, and the test continued until the subject chose to quit.

There is also evidence that supplementation with ALC may protect against physical and mental fatigue with researchers observing reduced physical and mental fatigue in hepatitis C patients Malaguarnera et al. It is generally recommended that this is taken on an empty stomach in the morning or early afternoon — try not to take Acetyl-L-Carnitine too late in the evening as it may make you feel more alert and therefore make it harder to sleep.

Higher dosages are unlikely to be beneficial as the excess is likely to be excreted and therefore wasted. To aid recovery athletes will often take acetyl-l-carnitine during periods of intensified training and then reduce or stop supplementation when training volume is decreased.

For an ergogenic effect: It is important to note that it still not completely clear whether acetyl-l-carnitine has a significant ergogenic effect. Therefore, it appears that if ALC has an ergogenic effect longer term supplementation may be required.

Research has found ALC to be safe and well tolerated with only mild side effects. Other potential side-effects include a rash and increased appetite.

Click here to view the acetyl-l-carnitine for endurance references. Home Endurance Supplements Acetyl-l-carnitine. Acetyl-l-carnitine and recovery from strenuous exercise One promising area of carnitine research is the role that L-carnitine supplementation has on recovery from endurance exercise and to reduce mental and physical fatigue.

How to take Acetyl-L-Carnitine? Blood samples were taken from the earlobes of the footballers both before the test and before the speed increase during the 1-minute interval , and the lactate La concentration was measured electroenzymatically.

The test was repeated after 1 week as a group of placebos P-3 and P The results show that 3 or 4 g of L-carnitine taken before physical exercise prolonged exhaustion. Abstract This study examined the effect of acute L-carnitine loading on the endurance performance of footballers. Publication types Randomized Controlled Trial.

Substances Performance-Enhancing Substances Vitamin B Complex Carnitine.

In a study by Colombani et al. Moreover, the study of Stuessi et al. Twelve subjects received either 2 g L-carnitine.

Two hours after administration, the subjects performed a constant-load exercise test cycling at their individual anaerobic threshold to exhaustion. They found that 2 g of L-carnitine taken 2 h before a first of two constant-load exercise tests had no influence on the second tests performed 3 h after the first test.

Also, one study used active healthy men. More especially, in a study by Parandak et al. Compared to the control group, those who took L-carnitine were found to have lower levels of certain markers that indicate muscle damage.

Table 1. Initially, in a study by Giamberardino et al. In a separate set of experiments carried out 8 months later, the possible effects of training on pain parameters and creatine kinase levels were also investigated in the same subjects. It is concluded that L-carnitine has a protective effect against pain and damage from eccentric effort.

Two papers from the same lab [22, 45] were also used in untrained male and female. After 3 weeks of L-carnitine supplementation loading, each participant then performed an acute resistance exercise.

They found that L-carnitine supplementation can reduce chemical damage and muscle soreness after physical exercise. On the contrary, there are some studies that referred in resistance trained subjects Table 1.

Two studies from the same lab [28, 50] investigated the effects of L-carnitine supplementation on recovery after resistance exercise.

Blood was also sampled before and after a squat protocol 5 sets, 15—20 repetitions. The results demonstrate that L-carnitine supplementation is effective in assisting recovery from high-repetition squat exercise. Effects of L-carnitine on Athletic Performance and Recommended Dosage Some athletes take L-carnitine to improve performance.

Table 2 Table 2. Some studies found that this supplementation improve athletic performance. More specifically, Gorostiaga et al. Also, in the study of Arenas et al. They found improvement in VO 2 max after L-carnitine administration.

Table 2 On the other hand, some studies have seen not improve of performance in distance runners. The study of Marconi et al. They suggested that this improvement is probably affected by variables, other than L-carnitine loading, of a physiological e.

Also, Colombani et al. Seven male subjects were given supplements of 2 g L-carnitine 2 h before the start of a marathon run and again after 20 km of the run. They found that acute administration of L-carnitine did not improve the physical performance of the endurance athletes during the run and did not alter their recovery.

In the study of Greig et al. The results of treatment with L-carnitine demonstrated no significant changes in VO 2 max or in maximum heart rate. Furthermore, in the study of Wachter et al. They found that supplementation of L-carnitine is not associated with a significant increase.

Moreover Cooper et al. The time of marathon run reduced by 3. Moreover, some studies used in untrained subjects and examined the effects of L-carnitine on athletic performance. DiSilvestro et al.

In the study of Shannon et al. They found improvements in VO 2 max. Also, in the study of Burrus et al. Bioavailability of L-carnitine in Athletes The bioavailability of L-carnitine from food can vary depending on dietary composition.

Less is known re-garding the metabolism of the acetylated form of L-carnitine, acetyl-L-carnitine; however, bioavailability of acetyl-L-carnitine is thought to be higher than L-carnitine.

In the studies of Sahajwalla et al. Finally, Rizza et al. Conclusions L-carnitine is unique in its essential role in energy metabolism, transporting fatty acids across the mitochondrial membrane for subsequent breakdown and energy generation [23].

The main limitation of the present systematic review is the small number of included studies that used distance athletes. Although, the vast majority of the studies recruited untrained or resistance trained athletes.

The main role of L-carnitine is to help populations with certain conditions achieve a higher level of exercise performance, particularly those with various dimensions of cardiovascular disease.

These results indicate that there is uncertainty in regards to how L-carnitine helps athletic performance. Found six studies that examined the effects of L-carnitine on athletic performance.

From these six studies, three studies in the literature showing beneficial effects of L-carnitine on performance of athletes [1, 19, 32]. On the contrary, three of studies have shown no effect of L-carnitine on performance [11, 12, 51].

However, it is clear that L-carnitine plays an important role on recovery from strenuous exercise [22, 45]. References [1] Arenas, J. FEBS Letters , 1 , Fisher-Wellman, K. Journal of International Society and Sports Nutrition , 3, International Journal for Vitamin and Nutrition Research , 79 3 , Journal of the American College of Nutrition, 17 3 , Annals of New York Academy of Sciences , , Clinical Therapy , 17 2 , The American Journal of Clinical Nutrition , 72 2 , SS.

Physiological Reviews, 63 4 , International Journal of Sport Nutrition and Exercise Metabolism. International Journal of Sport Nutrition , 3 1 , European Journal of Applied Physiology and Occupational Physiology, 73 5 , Journal of Sports and Science , 4 2 , International Journal for Vitamin and Nutrition Research, 75 1 , Genet Med , 12 1 , Clinical Pharmacokinetics , 42 11 , The J ournal of Biological Chemistry , , Effects of prolonged L-carnitine administration on delayed muscle pain and CK release after eccentric effort.

International Journal of Sports Medicine , 17 5 , International Journal of Sports Medicine , 10 3 , European Journal of Applied Physiology and Occupational Physiology , 56 4 , European Journal of Clinical Pharmacology , 35 5 , Metabolism , 59 8 , Medicine and Sport Science , 59, Obesity Reviews , 12 10 , Nutrition , 20 , Journal of Nutritional Science and Vitaminology Tokyo , 50 5 , Monatshefte für Chemie - Chemical Monthly, 8 , — Journal of Strength and Conditioning Research , 17 3 , Human Molecular Genetics , 8 12 , European Journal of Applied Physiology , 99 2 , European Journal of Applied Physiology Occupational Physiology , 54 2 , Journal of Renal Nutrition , 13 1 , In Vivo , 13 3 , British Journal of Clinical Pharmacology , 50 5 , Asian Journal of Sports Medicine 5 2 , Obesity Reviews , 17 10 , Annals of the New York Academy of Sciences , , In Shagass C, Josiassen RC, Bridger WH, Weiss KJ, Stoff D, Simpson GM eds : Biological Psychiatry.

Developments in Psychiatry Vol. New York: Elsevier Science Publishing, pp Journal of Pharmaceutical Sciences , 84 5 , Journal of Perinatal Medicine , 23 6 , Arzneimittelforschung , 38 12 , Cardiovascular Drugs and Therapy , 5 1 , Journal of Strength and Conditioning Research , 21 1 , Carnitine: a nutritional, biosynthetic, and functional perspective.

Molecular Aspects of Medicine , 25 , The Journal of Physiology , 18 , European Journal of Applied Physiology , 95 , International Journal of Sports Medicine , 15 4 , American Journal of Physiology.

Endocrinology and Metabolism , 2 , E Clinica Chimica Acta , The New England Journal of Medicine , 23 , Journal of the International Society of Sports Nutrition , 13 14 , International Journal of Exercise Science , 11 2 , B, , Does skeletal muscle carnitine availability influence fuel selection during exercise?

P roceedings of the Nutrition Society. Endocrinology and metabolism , 4 , EE Home About Us Terms and Conditions Privacy Policy Feedback Sitemap Contact Us. All rights reserved. Studies that examine the effects of L-carnitine in recovery after strenuous exercise. Table 2. Studies that examine the effects of L-carnitine on performance.

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The prevalence of sarcopenia increased steeply with age, reaching Muscle damage may occur during exercise, especially eccentric exercise. In the clearance of damaged tissues assist free radicals produced by neutrophils. Therefore, among other responses to exercise, neutrophils are released into the circulation.

While neutrophil-derived reactive oxygen species ROS play an important role in breaking down damaged fragments of the muscle tissue, ROS produced in excess may also contribute to oxidative stress for review see [ 47 , 48 ].

Based on the assumption that LC may provide cell membranes protection against oxidative stress [ 49 ], it has been hypothesized that LC supplementation would mitigate exercise-induced muscle damage and improve post-exercise recovery.

Since plasma LC elevates following 2 weeks of supplementation [ 21 , 22 ], short protocols of supplementation may be considered as effective in attenuating post-exercise muscle soreness.

It has been shown, through magnetic resonance imaging technique that muscle disruption after strenuous exercise was reduced by LC supplementation [ 37 , 51 ]. 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 ]. In Rebouche et al. Similar observations were noted in later human studies [ 56 , 57 ], with the peak serum TMAO observed within hours following oral administration of the tracer [ 56 ].

Prolonged LC treatment elevates fasting plasma TMAO [ 16 , 17 , 18 , 58 , 59 ]. Three months of oral LC supplementation in healthy aged women induced ten-fold increase of fasting plasma TMAO, and this level remained elevated for the further 3 months of supplementation [ 16 ].

Four months after cessation of LC supplementation, plasma TMAO reached a pre-supplementation concentration, which was stable for the following 8 months [ 60 ]. In Wang et al. Since diets high in red meat have been strongly related to heart disease and mortality [ 62 ], LC has been proposed as the red meat nutrient responsible for atherosclerosis promotion [ 8 ].

As a potential link between red meat consumption and the increasing risk of cardiovascular disease, TMAO has been indicated [ 8 ]. Numerous later studies have shown the association between increased plasma TMAO levels with a higher risk of cardiovascular events [ 63 , 64 , 65 , 66 ].

The recent meta-analyses indicated that in patients with high TMAO plasma level, the incidence of major adverse cardiovascular events was significantly higher compared with patients with low TMAO levels [ 67 ], and that all-cause mortality increased by 7.

The rise of plasma TMAO was on average three-fold compared with white meat and non-meat diets [ 70 ]. Conversely, habitual consumption of red, processed or white meat did not affect plasma TMAO in German adult population [ 71 ].

Similarly, a minor increase in plasma TMAO was observed following red meat and processed meat consumption in European multi-center study [ 72 ]. In the previous century, the underlined function of TMAO was the stabilization of proteins against various environmental stress factors, including high hydrostatic pressure [ 73 ].

TMAO was shown as widely distributed in sea animals [ 74 ], with concentration in the tissue increasing proportionally to the depth of the fishes natural environment [ 75 ].

Consequently, fish and seafood nutritional intake has a great impact on TMAO level in the human body [ 76 ], significantly elevating also plasma TMAO concentration [ 72 ].

Therefore, link between plasma TMAO and the risk of cardiovascular disease [ 8 ] seems like a paradox, since more fish in the diet reduces this risk [ 77 ]. Not only dietary modification may affect TMAO plasma levels.

Due to TMAO excretion in urine [ 56 , 57 ], in chronic renal disease patients, TMAO elimination from the body fails, causing elevation of its plasma concentration [ 78 ]. Therefore, higher plasma TMAO in humans was suggested as a marker of kidney damage [ 79 ]. It is worthy to note that cardiovascular disease and kidney disease are closely interrelated [ 80 ] and diminished renal function is strongly associated with morbidity and mortality in heart failure patients [ 81 ].

Moreover, decreased TMAO urine excretion is associated with high salt dietary intake, increasing plasma TMAO concentration [ 82 ]. The relation between TMAO and chronic disease can be ambiguous, involving kidney function [ 79 ], disturbed gut-blood barrier [ 83 ], or flavin-containing monooxygenase 3 genotype [ 84 ].

Thus, whether TMAO is an atherogenic factor responsible for the development and progression of cardiovascular disease, or simply a marker of an underlined pathology, remains unclear [ 85 ]. Carnitine preparations administered orally can occasionally cause heart-burn or dyspepsia [ 86 ].

It is worthy to mention that Bakalov et al. The strength of this review is a focus on the period of LC treatment, very important aspect often missed in many articles dealing with this supplement. This limitation is also magnified by the varied design of the studies available including different supplementation protocols and outcome measures.

There is also a high degree of heterogeneity among participants of the analyzed studies. Therefore, the results should be taken with caution, and more research is required before definitive recommendations.

Lasting for several years opinion that LC supplementation does not change metabolism, especially exercise metabolism, is based mostly on short-term supplementation protocols. Nevertheless, LC is still used by elite [ 9 ] and sub-elite [ 10 ] athletes. Recent studies suggest that LC supplementation may elevate muscle TC content; therefore, modify muscle fuel metabolism and performance during the exercise.

Due to insulin-mediated LC transport to the muscle, oral administration regimen should be combined with CHO. Because of LC poor bioavailability, it is likely that the supplementation protocol would take at least 3 months. Shorter period of supplementation may be effective in prevention of exercise-induced muscle damage, but not metabolic changes.

On the other hand, it is also clear that prolonged LC supplementation elevates fasting plasma TMAO [ 16 , 17 , 18 , 58 , 59 ], compound supposed to be pro-atherogenic [ 61 ].

Therefore, additional studies focusing on long-term supplementation and its longitudinal effect on the TMAO metabolism and cardiovascular system are needed. Bremer J. Carnitine--metabolism and functions. Physiol Rev. Article CAS PubMed Google Scholar.

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International journal of sports medicine , 17 5 , — Athletes were given a glass of fruit juice 1 hour before applying L-carnitine with the double-blind method.

Then, 12 participants were given 3 g of L-carnitine LK-3 and the remaining 14 were given 4 g LK Athletes began the exercise test at a running speed of 8 km·h and then continued at 10 km·h.

The speed was increased 1 km·h every 3 minutes, and the test continued until the subject chose to quit.