L-Carnitine really helps endurance athletes. If they consume the amino acid with high quantities of carbs for a few months, their muscles become more economical with glycogen and their work capacity increases.
Carnitine is a supplement that works wonderfully on paper, but not in practice. The mitochondria, the cellular power stations, need this amino acid to convert nutrients into energy. But carnitine means more energy and therefore a higher metabolic rate, so it's interesting for endurance athletes. Unfortunately, in most human studies on the subject L-carnitine has no effect. It seems as though muscle cells don't absorb the amino acid.
In 2007 a study was published in which it was clearly shown that muscle cells absorb L-carnitine at high sugar and insulin levels.
Now researchers at the University of Nottingham have published the results of a study in the Journal of Physiology, in which 14 active swimmers, triathletes, cyclists or runners were given a placebo and sports drink containing 80 g carbohydrates [Control] or the sports drink and 2 g L-carnitine L-tartrate, twice a day for 24 weeks. The 2 g L-carnitine L-tartrate contained 1.36 g L-carnitine.
During the supplementation period the amount of L-carnitine rose in the muscles of the carnitine group. When the researchers got the carnitine group to cycle for 30 minutes at 50 percent of their VO2max at the end of the 24 weeks, they noticed that the subjects used up less glycogen – i.e. they used more fat.
During a session in which they cycled at 80 percent of their VO2max, at the end of the half hour they had less lactate in their muscles. So the supplement had made their carbohydrate metabolism more efficient. And more effective, as their phospho-creatine:ATP ratio remained more or less stable, whereas the ratio in the control group dropped considerably.
The subjects in the creatine group were also capable of generating more energy in their session and were less tired at the end of it. You wonder what would happen if you combined carnitine supplements with interval training…
"These findings have significant implications for athletic performance", the researchers conclude. And no, they weren't paid by the supplements industry.
J Physiol. 2011 Feb 15;589(Pt 4):963-73.