At the age of 16, Heather Troupe received a diagnosis of chronic severe depression and a prescription for an antidepressant. Eight years and 20 pounds later, she was sleeping poorly, felt a lot of anxiety and had lost her therapist because of insurance complications.

'Exercise has been the biggest piece of the puzzle for me,' says Troupe, who is now a fitness instructor. 'It's a place for me to funnel all that extra energy -energy that would otherwise turn into sadness or anxiety.'