L-Carnitine gives football players the edge
Professional footballers have more energy if they take a couple of grams of L-carnitine before a match or a training session. Sports scientists at Aksaray University and Gazi University in Turkey published their findings in the Journal of Strength and Conditioning Research.Carnitine, mitochondria & endurance
Carnitine is found primarily in the muscle tissue of the heart. The liver and kidneys produce it from lysine, methionine and vitamins C, B3 and B6, but your body also gets it from dairy and meat products.

Carnitine plays a key role in the transport of fatty acids to the mitochondria, the power houses in the body's cells. The idea behind L-carnitine supplementation is that endurance capacity increases if cells burn fatty acids more easily as a result of the increased L-carnitine concentration.

This is a controversial idea however. There are studies that show that supplementation with several grams of L-carnitine per day has a mild ergogenic effect. But there are just as many studies in which for example 4 g carnitine has no effect whatsoever on fat burning [Eur J Appl Physiol. 2007 Jan;99(2):193-9.] or in which a month of supplementation leads to virtually no increase in the concentration of carnitine in the muscle cells [Am J Clin Nutr. 2000 Aug;72(2 Suppl):618S-23S.] - and thus suggest that carnitine can't have any effect at all.Study
The researchers performed an experiment designed to elucidate the effects of carnitine. They gave 26 professional footballers aged 17-19 either 3 g [LK-3] or 4 g [LK-4] carnitine and made them do an exertion test one hour later.

The test involved the players running for three minutes on a treadmill at a speed of 8 kph, followed by one minute of rest, then running for three minutes at a speed of 10 kph, followed by one minute of rest, etc. For the remainder of the test the researchers increased the speed at which the football players had to run by 1 kph.
The researchers went through the same procedure once again after giving both groups a placebo [P-3] [P-4].
During the 3-minute-long sets supplementation with 3g and 4g carnitine lowered the heart rate a little. In addition, the players gave themselves a slightly lower score for fatigue [Borg Scale]. The effects were small, but most of them were statistically significant.

"All those aforementioned results of the study are consistent with the finding that the installation of L-carnitine increases the effectiveness of endurance performance", the researchers write in their conclusion.

Another study
According to a human study done at the University of Nottingham, the body only absorbs carnitine well in combination with a few dozen grams of carbohydrates. If the Turkish researchers had got their subjects to take their carnitine supplements during meals, the results may have been more convincing.