Carnitine is a molecule involved in fatty acid translocation in the mitochondria (Figure 2 below). Theoretically, increased carnitine levels within the muscle would increase fatty acid metabolism thus sparing muscle glycogen. Glycogen sparing will improve endurance performance. However, research over the past 30 year was unsuccessful in elevating muscle carnitine levels with oral carnitine ingestion.
Few months ago a research group from the University of Nottingham Medical School, UK, showed elevated muscle carnitine levels after chronic carnitine ingestion in healthy subjects (Wall et al., 2011). Subjects were divided into two groups: a) the carnitine group, ingested 80g of carbohydrate (CHO) containing 2 gr of L-carnitine tartrate for 5,5 months, and b) the control group that received only CHO for the same period. Supplements were ingested at breakfast and 4 hours later. Physiological measurements and performance test took place before and at the end of the supplementation period.
The main findings were
- 21% increase in muscle carnitine level with oral ingestion
- lower muscle glycogen utilization during submaximal exercise in the carnitine group
- 35% improvement in the performance test in the carnitine group (Performance was defined as total work output in 30-min cycling in the laboratory).
Although this is a laboratory study, the findings suggest that chronic co-ingestion of L-carnitine and carbohydrate may improve endurance performance. This is the first study to show increased muscle carnitine levels with oral supplementation. To my opinion, these findings have important implications for athletic performance.
Wall et al (2011). Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. Journal of Physiology 589: 963-973.