Her stress hormones—cortisol and adrenaline—are surging. In her brain, cortisol is binding with receptors in the hippocampus, the seat of memory formation and learning. For now, this will hone her recall. But if she doesn't get her stress in check, over time, key connections between nerve cells in her brain won't function as well, impairing her memory and her ability to take in new information, and raising her risk for depression and anxiety.
More: Stress Busters
All she knows is that she's overwhelmed. So at lunch, she heads to the gym and hops onto the elliptical. As her heart begins to pound, levels of the feel-good neurochemicals serotonin, dopamine and norepinephrine rise in her body. So does brainderived neurotrophic factor (BDNF), a substance that may protect her brain from emotional disorders and repair damage that stress and depression cause. At the same time, opiate-like endorphins and endocannabinoids (similar to the other kind of cannabis) flood her system, leading to a sense of well-being.
People often throw around terms like "endorphin rush" or "runner's high" to explain the mood lift that can occur during or after a sweat session. But rather than a sudden burst of euphoria, research has found that a mere 20-minute workout can produce more subtle mood benefits that last as long as 12 hours. And when it comes to shorter bouts of activity, endorphins may actually have little to do with the mental perk-up. "When researchers blocked endorphins from runners' brains, some still said their mood improved after their workout," says John Ratey, M.D., author of Spark: The Revolutionary New Science of Exercise and the Brain.
More: Happiness in Motion
In part, the happiness effect may be due to endocannabinoids and BDNF; the latter may rise during exercise, prompting neural growth and repairing damage caused by ongoing stress and depression. "BDNF," Dr. Ratey says, "is like Miracle-Gro for your brain." When French researchers bred mice without cannabinoid receptors, the mice ran 30 to 40 percent less than normal mice, presumably because it wasn't as pleasurable for them.
Unlike those deprived mice, Woman A is feeling so good that she cranks up the elliptical. As she does, her body begins releasing gamma-aminobutyric acid, or GABA, a calming neurotransmitter. Not that she is calm, exactly; she's subjecting her system to a low-level form of stress. "Exercise raises your heart rate and triggers a surge of hormonal changes. Expose yourself to this 'stress' enough and your body builds up immunity to it. Eventually, it will get better at handling the rest of life's stressors," says clinical psychologist Jasper Smits, Ph.D., coauthor of Exercise for Mood and Anxiety. But stay sedentary and your body can become more sensitive to stress, so even minor triggers leave you tied up in knots.