We love how author/comic Tim Kreider says he is never anxious or afraid when riding his bike in Manhattan traffic. "You are forced, under pain of death, to quit all that silly ideation and pay attention. It's meditation at gunpoint,"
he writes. Any cardio workout involves the release of the hormone serotonin, which increases concentration and calms the amygdala
, the fear center of the brain, says John Ratey, MD, a Harvard Medical School psychiatrist and author of the book Spark: The Revolutionary New Science of Exercise and the Brain
. But if you're streaking through the streets on your racing red Bianchi (or doing anything that gives you a similar rush), you also get an extra boost of norepinephrine, a neurotransmitter that has the mind-sharpening, energizing effects of Ritalin and Adderall. You're running a built-in survival program, Ratey says. You're alert, in control and completely present—you're not worrying about anything else for once. (Break your anxiety cycle but not your skull: Remember to wear a helmet.)