Exercise can make you happy …but only if you do it enough.
When you work out, your brain perceives exercise as stress and puts you into "fight or flight" mode, releasing endorphins to block feelings of fear or pain. If you're out for a run rather than, say, being chased by a lion, those endorphins make you happy.
But studies reveal that working out three times a week isn't good enough to make that happy feeling last. You need to work out for at least 20 minutes every day to keep those good vibes going.