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strong man folding arms interested in the study that nutritionists at the Korean Chonbuk National University published in 2001 in the Journal of Nutritional Science and Vitaminology. Researchers examined the effects of experimental sports drinks containing high quantities of both caffeine and L-carnitine on rugby players.  

Each of the five test subjects had five years on training experience minimum. Subjects were not allowed to use drugs or doping supplements and were asked to not use any caffeine products during the study. On four different occasions, and on separate days, athletes were given 250ml of a sports drink containing different active ingredients.

On one occasions the drink contained no active ingredients. [CON] On a second occasion the drink contained 5 mg caffeine per kg body weight for each athlete [CAF]. On the third occasion the drink contained 15 g L-carnitine [CAR], and on the fourth occasion the drink contained both 5 mg caffeine per kg body weight and 15 g L-carnitine [CAF+CAR].

Caffeine prevents adenosine from binding to its receptors in the brain and thus reduces drowsiness. Adenosine is an inhibitory neurotransmitter, whose role is promoting sleep and suppressing arousal. The levels gradually increase in the body throughout the day while you’re awake. By inhibiting that process caffeine has a stimulatory effect. When caffeine inhibits the adenosine (cAMP) its effects are prolonged and the response throughout the body in amplified. For the heart, this response is the release of nor-epinephrine along with epinephrine, triggering the release of glucose from energy stores, accelerated heart speed, and increased force of muscle contractions. As an end result muscles are prepared for more explosive, violent contractions and are able to work harder for longer. During this time more fat and glucose are metabolized into the bloodstream for muscular action.

L-Carnitine has a less intrusive effect. It aids the mitochondria, the cell’s energy powerhouses, to facilitate fatty acid utilization into energy. This increases energy levels for long-term aerobic activity. By providing more fat to the muscles, carnitine makes accessible an otherwise unavailable energy source.

An hour after intake the test subjects were made to cycle: first they rode for 45 minutes at 60 percent of their VO2max. That’s a speed at which you can just keep up a conversation. After that the athletes upped their speed to 80 percent of their VO2 max, a speed at which it’s no longer possible to keep talking. According to the researchers’ measurements, the athletes in the CAF+CAR group kept up the high speed for twice as long as the athletes in the CON group.

Analyses of the athletes’ blood suggested that the cocktail works in the way the theory would lead one to imagine. Caffeine chases fatty acids out of the fat cells, and L-carnitine induces the muscles to burn more fatty acids.

“This study showed that carnitine ingestion could promote fat oxidation and endurance performance in athletes, and especially these ergogenic effects of carnitine congested with caffeine more than a single bout of carnitine”, the Koreans conclude.

The doses used were high. If you are sensitive to caffeine, a dose of 5 mg per kg bodyweight can cause psychological side effects. Some people also report mild gastrointestinal complaints after taking 15 g L-carnitine.


J Nutr Sci Vitaminol (Tokyo). 2001 Dec;47(6):378-84.