The New York Times‘ fitness writer seems surprised that intense exercise is more effective than milder exercise. A new study found one mechanism:
At Scripps, the scientists had been focusing on catecholamines and their relationship with a protein found in both mice and people that is genetically activated during stress, called CRTC2. This protein, they discovered, affects the body’s use of blood sugar and fatty acids during moments of stress and seems to have an impact on health issues such as insulin resistance.
The researchers also began to wonder about the role of CRTC2 during exercise.
Scientists long have known that the sympathetic nervous system plays a part in exercise, particularly if the activity is intense. Strenuous exercise, the thinking went, acts as a kind of stress, prompting the fight or flight response and the release of catecholamines, which goose the cardiovascular system into high gear. And while these catecholamines were important in helping you to instantly fight or flee, it was generally thought they did not play an important role in the body’s longer-term response to exercise, including changes in muscle size and endurance. Intense exercise, in that case, would have no special or unique effects on the body beyond those that can be attained by easy exercise.
But the Scripps researchers were unconvinced. “It just didn’t make sense” that the catecholamines served so little purpose in the body’s overall response to exercise, said Michael Conkright, an assistant professor at Scripps, who, with his colleague Dr. Nelson Bruno and other collaborators, conducted the new research. So, for a study published last month in The EMBO Journal, he and his collaborators decided to look deeper inside the bodies of exercising mice and, in particular, into what was going on with their CRTC2 proteins.
To do so, they first bred mice that were genetically programmed to produce far more of the CRTC2 protein than other mice. When these mice began a program of frequent, strenuous treadmill running, their endurance soared by 103 percent after two weeks, compared to an increase of only 8.5 percent in normal mice following the same exercise routine. The genetically modified animals also developed tighter, larger muscles than the other animals, and their bodies became far more efficient at releasing fat from muscles for use as fuel.
These differences all were the result of a sequence of events set off by catecholamines, the scientists found in closely examining mouse cells. When the CRTC2 protein received and read certain signals from the catecholamines, it would turn around and send a chemical message to genes in muscle cells that would set in motion processes resulting in larger, stronger muscles.
In other words, the catecholamines were involved in improving fitness after all.
What this finding means, Dr. Conkright said, is that “there is some truth to that idea of ‘no pain, no gain.’”