Study: Tired muscles

In my previous post on lactic acid, I mentioned that it is no longer considered a factor in muscle fatigue. One of the leading theories holds that it is the hydrogen ion released during the conversion of lactic acid to lactate that causes fatigue. As the hydrogen ions accumulate, the pH of the muscle cells drops (from about 7.1 to 6.4) and the thinking held that this causes the fatigue. Other suggested causes of tiredness have been the accumulation of phosphate and the loss of potassium.

Now there is a new study published in Proceedings of the National Academy of Sciences that indicates muscle fatigue is caused by calcium leaking into the cells. It's pretty heavy reading but the New York Times has a good article that explains the findings in lay terms.

It is the release of calcium in a muscle cell that actually makes it contract. When the calcium is reabsorbed, the muscle relaxes. But it's an imperfect process and some of the calcium leaks out, which keeps the muscle from contracting at full force. Worse, that calcium also helps an enzyme eat away at the muscle fibers.

The interesting part of all this is that it may lead to new ways for athletes to fight off fatigue. They've already developed a drug that plugs the calcium leaks and allows mice to exercise 20% longer. But we're still many years from having a magic pill that will give us the same benefit. And no, eating more calcium isn't the answer either.