Because we've heard it so often -- and because we feel pretty good after we exercise ourselves -- we've never examined the axiom that exercise floods the brain pan with miracle motes known as endorphins, triggering a natural high. But when we heard that human and rat studies on exercise and mood called that maxim into question, we stopped to take a look.
First, the basic stuff: "We know [from studies] that exercise is good for the brain," says Daniel Galper, senior research associate in the mood disorders research program and clinic at the University of Texas Southwestern Medical Center in Dallas. Brain imaging studies show that exercise boosts activity in the brain's frontal lobes and the hippocampus. But those effects are complex and, says Galper, "it is hard to identify the physiological processes" responsible for the benefits. In the 1970s researchers detected a significant rise of endorphins, morphine-like peptides, in the blood of marathon runners, and quickly tied this to the "runner's high" so widely claimed during that era.
But, says John Ratey, clinical associate professor of psychiatry at Harvard Medical School, later research in rodents and people showed that "endorphins don't cross into the brain easily. They get metabolized." (Endorphins do reduce pain, which is why you get a lower pain response when you exercise.) Still later research showed that physical activity promoted the creation and survival of neurotransmitters -- molecules that shuttle messages between neurons. In animal studies, exercise boosted levels of three neurotransmitters -- serotonin, dopamine and norepinephrine -- that are associated with elevated mood. (Many antidepressant drugs, including Prozac, are designed to raise the concentration of those molecules in the brain.) Still, studies have not concluded that the effect causes positive emotions.
On a more practical level, consensus is also lacking on how much exercise yields emotional benefit. "Some studies have shown that a five-minute burst of exercise improved mood," Ratey says. A study at Duke University last year showed that walking for 30 minutes had a significant effect in depressed patients. But those results were self-reported and not conclusively tied to chemical changes in the brain.
Exercise-related chemical processes in the body happen fast, Galper says, but the fuller antidepressant effect can take many weeks.
More recent research in rodents and humans has shown that exercise promotes the production of a beneficial substance called brain-derived neurotrophic factor, or BDNF.
BDNF appears to cause antidepressant effects, says Madhukar Trivedi, psychiatry professor at UT Southwestern and principal investigator of an ongoing study on exercise and depression. Ratey agrees. "I call [exercise] 'Miracle Grow for the brain.' Exercise keeps these cells healthy in a way that even playing chess [and other highly cognitive activities] does not."
The takeaway? Self-reported evidence links exercise and emotional uplift. But next time someone launches into the endorphin speech, scurry to the rat wheel, slap on the iPod and tune out.
From: www.revolutionhealth.com
Posted in: Exercise