Your mind is in everything you do. You forget that it doesn't matter how big your muscle fibers are, it's still up to the central nervous system to use them (which is made of the spinal cord and the brain). Ever seen people making strength gains while cutting? That's not because their muscles are getting stronger, it's because their CNS is getting more efficient. And the CNS is obviously affected by emotion (hello, brain?

). If you're feeling like crap you'll have a crappy workout. If you're feeling "electric" you'll be lifting like a madman.