Feel like your workouts aren’t going so well? Perhaps carnitine supplements may be of use to reach your fitness goals.
The compound carnitine is synthesized from amino acids lysine and methionine. Its role is to transport fatty acids from the cytosol to the mitochondria to help break down lipids and fats in order to create metabolic energy. The majority of carnitine is found in skeletal muscle, helping maintain co-enzyme A by creating acetylcarnitine during high intensity exercise.
In a study done by Maastricht University in the Netherlands, researchers Benjamin Wall, Francis Stephens, Dumitru Constantin-Teodosiu, Kanagaraj Marimuthu, Ian Macdonald and Paul Greenhaff hypothesized that chronic ingestion of L-carnitine and carbohydrates would increase skeletal muscle total carnitine content in healthy participants, generating various positive metabolic effects of muscle carnitine loading that would lead to an improvement in high intensity exercise performance.
For the double-blind experiment, 14 healthy, athletic male participants were used. Two weeks before the start of the trial, the participants were pre-tested for maximal oxygen consumption so individual exercises could be determined to use 50% and 80% of their maximal oxygen uptake.
For the trial phase, the subjects were to undergo the experimental protocol on three occasions, 12 weeks apart. Blood samples were collected to assess blood glucose, serum insulin and plasma total cholesterol concentration. The participants exercised for 30 mins on a cycle ergometer at 50% maximal oxygen intensity, followed by 30 mins of exercise at 80% maximal oxygen consumption. Immediately after the exercises, the participants performed a 30-min work output performance test to measure endurance and performance.
After the first experimental visit, the participants were randomly assigned to two treatment groups. The control group consumed 700 mL of a beverage containing 80 grams of carbohydrate polymer twice daily for 168 days.
The experimental group consumed the same amount of beverage but with an additional 2 grams of L-carnitine tartrate, at the same frequency. On every visit, the same exercise protocol was conducted as the first visit. Blood samples and muscle biopsy samples were also collected from the participants throughout.
The effect of L-carnitine on muscle total carnitine content and exercise performance
After evaluating the data, the researchers found that after 24 weeks muscle total carnitine content was 30% more in the carnitine group than the control, meaning a 21% increase from baseline.
This is the first study conducted that demonstrated muscle carnitine content can be increased by dietary intake in humans. It also showed carnitine plays a role in the fuel metabolism of skeletal muscle, dependent on intensity of exercise.
The researchers also found that work output was 35% greater for the carnitine group compared to the control, by the end of the trial. This represented a 11% increase from baseline measures. By increasing muscle total carnitine content, muscle carbohydrate use is reduced during low intensity exercise. For high intensity exercise, muscle carnitine reduces muscle anaerobic energy due to its enhanced generation of glycolytic, pyruvate dehydrogenase complex and mitochondrial flux.
Working as a combination, these metabolic effects lead to a reduced perceived effort but increased output, helping improve exercise performance.