Awesome research study: even if you are forced to smile i.e. you know you are faking it, your stress is lessened versus a neutral or frowning expression.  “Smile while you are stressed, genuinely if possible. But faking — i.e., smiling with just your mouth — may still be worth your effort. Doing so does not reduce stress in the moment, but it speeds recovery when a stressful experience is over.”  Because the feeling of stress is lessened, smiling during exercise allows one to work harder and longer.

Smile On, my friends.