Carnitine is an amino acid made in the body and is best known for assisting with the breakdown of fats for energy production.

In a new study, male athletes were given 2 grams of L-carnitine plus 80 grams of carbohydrate and then exercised for three separate cycling sessions.  The first was 30 minutes at 50% maximal oxygen consumption (Max Vo2), then 30 minutes at 80% maximal oxygen consumption, then 30 minutes of maximal work output. They were compared to another set of athletes who were only given carbohydrate and performed the same cycling sessions.

The athletes had their muscles biopsied (ouch!) at rest and immediately after each cycling session. 

The Results:

• At 24 weeks, after cycling at 50% max Vo2, those cyclists supplementing used 55% less glycogen (the storage form of glucose) compared to those not taking the supplement.

• After cycling at 80% max Vo2, the supplement group showed a decrease in lactate (lactic acid) in their muscles  by 44%.  Lactate is considered a by-product of less than efficient ATP energy production when oxygen isn’t  utilized (anaerobic). 

• The max work output group increased output by 11% compared to the start of the study, while those not taking the supplement showed zero improvement. 

The study researchers concluded that carnitine supplementation can result in a muscle glycogen-sparing effect during low intensity exercise (such as that done during endurance events). This is consistent with an increase in lipid (fat) burning which is always the goal in endurance events.  Supplementation with this amino acid can also reduce anaerobic ATP production at higher intensity exercise.  These findings are associated with improved exercise performance.  

Reference:

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: the dual role of muscle carnitine in exercise metabolism. J Physiol. 2011 Jan 4.