Whether you're dragging yourself to the gym for the first time in god-knows-how-long or just pushing yourself through a tougher-than-normal workout, what's probably way more important than your lung capacity or the size of your biceps is what's going on inside your head. After all, thoughts like This sucks and I can't do this can be self-perpetuating. And anyway, experts say that psyching yourself up for something challenging can do wonders for your physical performance. Just imagine your inner cheerleader (picture “Joy” from Inside Out), holding an oversized megaphone, ready to drown out the bad noise with any of these power-finding mantras we got from a very reliable source.