by Thomas Incledon, PhD(c), RD, LD/LN, RPT, NSCA-CPT, CSCS
What’s this? Not the same old news about the acid L-carnitine! Well hold on because recent research has yielded some new findings for this old dog.
Some Background
L-carnitine is commonly found in red meats and dairy products. It is generally assumed that the body can produce carnitine if it is low in the diet. Cells in the liver, kidney and brain produce the amino acid which then travels to heart and skeletal muscle. The primary function in the body is to transfer fatty acids into mitochondria so that it can be used for energy.
The Old News
It used to be that every magazine was running an article on how L-carnitine could burn fat. The articles were based on the fact that carnitine helps transport fatty acids to locations within cells where they can be burned for fuel. The ingestion of carnitine was also speculated to increase the use of fatty acids for energy and spare muscle glycogen, thereby increasing endurance performance. Few studies supported this notion, so researchers began to investigate the effects of L-carnitine on aerobic performance. When runners were given four grams per day for two weeks it was found that their maximal oxygen consumption increased [1]. When endurance trained subjects were given two grams per day for 28 days, it was found that they used less oxygen at the same exercise intensity. These results seemed to support the notion the L-carnitine could improve endurance performance. However, later studies did not seem to agree with these findings. Researchers found that when they gave L-carnitine to subjects it had no effect on concentrations of carnitine in exercising muscles [2, 3]. If you subscribed to the earlier theories, it would be expected that in order for L-carnitine to improve exercise performance, it would have to get inside the muscle. Yet doses of four to six grams per day had no effect on muscle concentrations. This indicated that carnitine concentrations inside the cell do not limit exercise performance. The obvious question then is how does L-carnitine work to enhance performance? Recent evidence indicates that this may have nothing to do with fatty acid oxidation.
Research on Muscle Damage
Lifting weights has its price. When our muscles shorten and lengthen against tension, some of the proteins inside the cells get damaged. The lengthening of a muscle against tension is called an eccentric contraction. The intensity and/or volume of eccentric muscle actions are directly related to delayed muscle soreness (DOMS) and muscle damage. DOMS and muscle damage are not responsive to most common analgesic agents. It was surprising to find that when subjects were given three grams per day of L-carnitine for three weeks that it exerted protective effect against DOMS and muscle damage from eccentric effort [4]. This effect was mainly attributed to the ability of L-carnitine to increase blood flow to the working muscle which improved energy production and washed out metabolic waste products. Subjects in this study were untrained so it wasn’t clear what this would mean to more advanced lifters. A more recent study used ten resistance-trained men [5]. Researchers investigated the effects of L-carnitine L-tartrate (LCLT) on markers of muscle energy catabolism, free radical formation, and muscle tissue disruption after performing the squat exercise. Two grams per day of LCLT for three weeks was able to reduce muscle disruption as assessed by MRI scans and blood markers and reduce markers of free radical production. The researchers concluded that LCLT supplementation is effective in assisting recovery from a high-repetition squat exercise.
Research on Force Production
Animal data and human data don’t always yield the same results. It is interesting however to examine some studies on dogs because they may apply to humans. Researchers realized that since skeletal muscle is rich in carnitine and because carnitine transport into muscle is slow, its effect must be exerted elsewhere [6]. Using the latissimus dorsi of a dog, L-carnitine improved contractile force by 34% while being artificially stimulated. The effect of carnitine was acute and specific to L-carnitine, since neither D-carnitine nor the structural analogue choline had an effect on contractile force. Glucose stimulated insulin release abolished the effect of L-carnitine. In another canine study, carnitine was again proven to increase force by about 31% [7]. These researchers hypothesized that during muscle stimulation, a relative carnitine deficiency occurs in cells of the blood vessels. Carnitine may improve blood flow and hence allow for the increased production of energy and removal of waste products. This is supported by the fact that carnitine has a stronger effect on untrained muscle, which has less capillaries, and increases blood flow during exercise. These dogs were artificially stimulated, so it isn’t exactly the same as sending them to the gym to lift weights. However, they did experience an increase in blood flow that resulted in an increase in force production. It is known that carnitine increases blood flow in humans, so perhaps an increase in force could also occur. This area certainly needs to be investigated.
Applying the Research
Overall we know some studies show that L-carnitine may increase maximal oxygen consumption during endurance-type exercise, may decrease the need for oxygen during submaximal exercise, will most likely increase blood flow, and most likely decrease muscle damage and soreness. How well this translates into performance improvements is not certain. The doses that have been studied range up to about six grams. A prudent strategy if you want to incorporate this product into your supplement regimen is to start with two grams for three weeks and keep track of your muscle soreness and strength gains in the gym. Ingest the carnitine with meals about three hours before training. Keep track of your progress and feel free to send me an email to let me know what happens.
References
1. Marconi, C., et al., Effects of L-carnitine loading on the aerobic and anaerobic performance of endurance athletes. Eur J Appl Physiol, 1985. 54(2): p. 131-5.
2. Barnett, C., et al., Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling. Int J Sport Nutr, 1994. 4(3): p. 280-8.
3. Vukovich, M.D., D.L. Costill, and W.J. Fink, Carnitine supplementation: effect on muscle carnitine and glycogen content during exercise. Med Sci Sports Exerc, 1994. 26(9): p. 1122-9.
4. Giamberardino, M.A., et al., Effects of prolonged L-carnitine administration on delayed muscle pain and CK release after eccentric effort. Int J Sports Med, 1996. 17(5): p. 320-4.
5. Volek, J.S., et al., L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress. Am J Physiol Endocrinol Metab, 2002. 282(2): p. E474-82.
6. Dubelaar, M.L., C.M. Lucas, and W.C. Hulsmann, Acute effect of L-carnitine on skeletal muscle force tests in dogs. Am J Physiol, 1991. 260(2 Pt 1): p. E189-93.
7. Dubelaar, M.L., C.M. Lucas, and W.C. Hulsmann, The effect of L-carnitine on force development of the latissimus dorsi muscle in dogs. J Card Surg, 1991. 6(1 Suppl): p. 270-5.
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