Quote from this interesting study:

“The mere act of kindness, or one of evil, can boost willpower and physical strength, a new study suggests.

The results, based on three experiments, show that those who performed good deeds, or envisioned themselves acting charitably, were able to hold a weight or squeeze a hand grip significantly longer than those who didn’t perform or think about such deeds.

But evil acts appeared to confer similar and perhaps even greater superpowers. “

Source of Story

http://www.livescience.com/culture/etc/090929-good-evil-the-fine-genetic-line.html