14 DAY TRIAL // Every skeletal muscle fatigues, more or less rapidly, but why is that? It has been believed for almost a century that muscle fatigue is caused by lactic acid, produced during exercise and thought to impair contractile proteins. But studies made in the last years showed that, at body temperatures, very little acid stores inside muscle cells, and in fact, this molecule boosts endurance. Calcium has turned into the main suspect.
A new research points that leaky calcium channels can provoke muscle fatigue. During normal muscle function, a neuron causes the release of calcium within a muscle cell; the calcium makes the muscle proteins contract. The protein calstabin shuts the calcium channels during the contraction until they are 'told' to open.
The team led by physiologist Andrew Marks of Columbia University has reported that calstabin does not work well in mice with heart failure. The leaking leaves the heart cells without the calcium supply necessary for contraction, causing heart exhaustion. Now, the team has checked if the same thing happens in case of muscle fatigue.
The researchers have put lab mice to swim daily for two 90-minute sessions, for 2 weeks. The group of control mice swam 15 minutes twice daily. When the team analyzed muscle samples from the mice, similarly to failing heart muscle, the calcium channels of the mice that made more physical exercise had turned chronically leaky and they had to rest for days in oder to recover. "When the team analyzed the calcium-channel structure in muscle samples from 12 elite athletes before and after a series of intense cycling sessions, their calcium channels had begun to undergo changes that were 'totally parallel' to what had happened in the mice," Marks told ScienceNow.
The team has made a drug that could ease heart exhaustion, and a similar drug was tested on mice. The chemical functions by increasing the attachment of calstabin to calcium channels.
On the drug, "the high-exercise mice could run 10% to 20% longer on a treadmill than controls could, even after 3 weeks of extreme exercise," wrote the authors.
"The work is significant in the context of extreme exercise and may eventually help elite athletes improve their performance. It may even help ease pathological muscle fatigue in ailments such as emphysema, which involves exhaustion of the diaphragm. Still, muscle fatigue is complex and this one mechanism is only a part of the process. The average person exercising on weekends will get tired well before the calcium leak brings him down," muscle physiologist Christopher Ward of the University of Maryland, in Baltimore, told ScienceNow.