The Best Workout for Your Mood

If you think endorphins are to thank for the emotional high you experience after exercising, you're not wrong. But you're not totally right either.

Endorphins are natural painkillers that get released in the brain when your body is under stress, says Tiina Saanijoki, PhD, a neuroscientist and research manager at the University of Turku and Åbo Akademi University in Finland. People often think endorphins kick in with any type of exercise. The truth is, they come into play only during activity done at certain intensities or for certain durations, and those specs differ from person to person, says Saanijoki. (In Saanijoki's recent study, her team found that a brief bout of HIIT triggered more of an endorphin rush than an hour of moderately intense cycling did. And some participants saw a surge in endorphins at lower intensities than others did.)