L-Carnitine plus carbohydrate improves muscle function in endurance athletes

June 03, 2011

After you eat, insulin stores sugar in your muscle in a form known as glycogen. The glycogen is a storage form of fuel readily available for the muscle to use and during exercise glycogen is broken back down into sugar that is used for fuel. Unfortunately we have a limited amount of glycogen stored in our muscle.

In endurance exercise after long periods of exertion the athlete goes into glycogen debt where muscle glycogen can be almost totally spent as fuel; this is referred to as hitting the wall where the muscle has no more readily available energy reserve. This often occurs in runners, cyclists, cross country skiers and other endurance athletes who perform for a long time without eating. When experiencing glycogen debt, athletes often experience extreme fatigue to the point that it is difficult to move.

In this study researchers from the University of Nottingham Medical School enrolled 14 healthy buff men in their mid twenties.  They cycled at 50% of their VO2max for 30 minutes, then cycled at 80% for 30 minutes and then performed a 30 minute performance trial measuring work output (how much endurance they had left). They did this 3 different times separated by 3 months each time.

After the first visit the men consumed either 80 grams of carbohydrate (CHO) or 80 grams of CHO plus 200mg L-Carnitine twice a day for the duration of the study (24 weeks). Muscle Carnitine increased by 21% in the Carnitine group but not in the CHO only group. L-Carnitine improved the supply of energy to muscle by reducing the amount of glycogen used by muscle during endurance exercise by 55% converting the energy source to muscle fat; this is great because fat is a great source of energy and there is limited glycogen available. At 80% VO2max muscle lactate was 44% lower. This is also great because this translates to a lower production of lactic acid; lactic acid acidifies the muscle and causes it to seize blocking performance and leading to cramping. The Carnitine group improved work output by 11% from baseline in the performance trial while the CHO only group showed no change and there was a distinct improvement in the balance of the ratio of ATP (the energy molecule) to phosphocreatine in the Carnitine group; this shows improvement in energy supply efficiency and energy reserve. The study is published online ahead of print in the Journal of Physiology.