Exercise reduces physical problems due to stress. This makes sense because joint movement increases serotonin production. Serotoninis a neurotransmitter (a chemical that enables nerve cells—especially in the brain, to communicate with each other). Many anti-depressant drugs act to increase serotonin activity. According to a 1999 study published in Annals of Behavioral Medicine, people who exercise have fewer physical problems due to stress. During stressful times, college students who exercised regularly experienced 37% fewer physical symptoms and 21% less anxiety than those who did not exercise frequently. To quote the researchers, exercising “allows for a temporary escape from the pressure of stressors and thus acts as a kind of ‘rejuvenation’ process.”