MCT 1 – Lactic Acids Best Friend: How MCT 1 Helps You Beat Running Fatigue

By Rick Morris

Running requires a lot of energy, but I don’t need to tell you that. When you’re fighting through the debilitating effects of fatigue in the final mile of a 10K it becomes obvious that energy production is a high priority for a runner. You are probably already aware that much of that energy comes from glycolysis - the breakdown of your body’s glucose stores.

A necessary part of glycolysis is the production of lactic acid. Every molecule of glucose that’s processed produces two molecules of lactic acid. It was once thought that the lactic acid produced was a dead end waste product that was the primary cause of running fatigue. Now we know different – that lactic acid is actually sucked up by your muscle cells and used to produce more energy. Since each molecule of glucose breaks down into two lactic acid molecules, high intensity running produces a considerable amount of lactic acid. By the way, lactic acid is composed of lactate and a hydrogen proton. It is that pesky proton that is still believed to contribute, at least in part,  to running fatigue. All of that lactic acid creates a large amount of potential energy. The trick is to get that lactate into muscle cells that need it and out of those that don’t. That’s were MCT 1 comes in.

MCT 1 is more specifically called a monocarboxylate transporter. They are basically your cellular delivery drivers. They pick up lactate and move it in and out of muscle cells. There is more than one MCT. Researchers have actually discovered eight of them as of the writing of this article. There are two that are of most interest to runners – MCT 1 and MCT 4. Both MCT 1 and MCT 4 are found in muscle cells. Your more oxidative slow twitch or red muscle fibers contain a lot of MCT 1 but only a small amount of MCT 4.  In contract, your more glycolytic fast twitch or white muscle fiber contain little or no MCT 1. Instead, your fast twitch fibers contain more MCT 4. Your slow twitch fibers contain more MCT 1 because that compound is good at transporting lactate into a red muscle cell that needs a lot of lactate to produce energy. On the other hand your white or fast twitch muscle cells don’t have the capability to use the lactate that is produced. Your white muscle cells need to get rid of the excess lactate and the MCT 4 is very good at transporting lactate out of cells.

The system is remarkably efficient. Your white muscle cells need a way to get rid of accumulating lactate so more MCT 4 is activated to move the lactate out. Your red muscle cells need the lactate to produce more energy. So more MCT 1 is activated to bring the lactate into the red cells, where it’s processed to produce large amounts of energy. Your white cells are happy; your red cells are happy and your body is happy because it’s maintaining a level of homeostasis or “balance”.

At fast running paces your body produces large amounts of lactic acid. So, you need a lot of MCT 1 to transport that lactate into your red muscle cells. If you can produce more MCT 1 you will be able to run further at faster paces. How do you build more MCT 1? Really simple – you run. Both moderate and high paced training has been shown to activate more MCT 1, but is there an ideal pace for building the most MCT 1. Yep – there is. Numerous studies have agreed that high intensity training is the best way to increase MCT 1 levels. One recent study showed that a 7 day program of intense bicycle training increased MCT 1 by 18%. Another concluded that intense knee extensor exercise increased MCT concentration by a whopping 76% and MCT 4 by 32%. A 2007 study done in Norway on cross country skiers had similar results with the researchers concluding that training at high intensities is the most efficient way to increase MCT 1 levels.

There are many specific workouts you could perform to increase your MCT levels. Just make sure you do them at a high intensity pace – 10K pace or faster. Some examples are 2 x 20 minute repeats at 10K pace or 8 x 1 minute repeats at nearly all out pace. If you are following a multi-pace training plan that includes two quality workouts per week, at 10K pace or faster, you are probably already doing a good job of maintaining or improving your MCT levels. If not, you should consider adding high intensity training into your routine. Remember that MCT 1 is lactic acids best friend.

References:

Effect of training intensity on muscle lactate transporters and lactate threshold of cross-country skiers. Acta.Physiol Scand. 2001 Oct;173(2):195-205

Effects of high intensity training on MCT1, MCT4 and NBC expressions in rat skeletal muscles: influence of chronic metabolic alkalosis. Am J Physiol Endocrinol Metab. 2007 Oct:293(4): E916-22. Epub 2007 Jul 3

Lactate transport in skeletal muscle – role and regulation of monocarboxylate transporter. J Physiol 1999;517;633-642