The types of molecules also ranged widely, with some involved in fueling and metabolism, others in immune response, tissue repair or appetite. And within those categories, molecular levels coursed and changed during the hour. Molecules likely to increase inflammation surged early, then dropped, for instance, replaced by others likely to help reduce inflammation.
“It was like a symphony,” says Michael Snyder, the chair of the genetics department at Stanford University and senior author of the study. “First you have the brass section coming in, then the strings, then all the sections joining in.”
Interestingly, though, different people’s blood followed different orchestrations. Those who showed signs of insulin resistance, a driver of diabetes, for instance, tended to show smaller increases in some of the molecules related to healthy blood sugar control and higher increases in molecules involved in inflammation, suggesting that they were somewhat resistant to the general, beneficial effects of exercise. The levels of other molecules ranged considerably in people, depending on their current aerobic fitness.
Over all, the researchers were taken aback by the magnitude of the changes in people’s molecular profiles after exercise, Dr. Snyder says. “I had thought, it’s only about nine minutes of exercise, how much is going to change? A lot, as it turns out.”
This study was small, though, and looked at a single session of aerobic exercise, so cannot tell us anything about the longer-term molecular effects of continued training or of how, precisely, changes in molecular levels subsequently alter health. It also did not include young volunteers under 40.
Dr. Snyder and his colleagues are planning follow-up experiments with more volunteers and sustained exercise programs. They hope to establish whether certain molecular responses to exercise might distinguish people who would benefit from emphasizing resistance exercise over endurance training and whether specific molecular profiles indicate who has higher or lower aerobic endurance. This information could allow physicians and researchers to check fitness with a simple blood draw instead of a treadmill stress test.