Kurt Gray, a doctoral student in psychology at Harvard University carried out two studies demonstrating the power of moral thought on strength and endurance.

In the first study he gave participants a dollar and told them they could keep it or give it to charity. In a later test, those who gave their dollar to charity were able to hold a weight for 10 seconds longer than those who kept it for themselves.

"People perceive those who do good and evil to have more efficacy, more willpower, and less sensitivity to discomfort," Gray says. "By perceiving themselves as good or evil, people embody these perceptions, actually becoming more capable of physical endurance."

In the second study, participants held a weight while writing fictional stories of themselves either helping another, harming another, or doing something that had no impact on others. As before, those who thought about doing good were significantly stronger than those whose actions didn't benefit other people.

The bad news, however, is that turning to the Dark Side can make you even more powerful. In Gray's second study, participants who imagined harming someone else were able to hold the weight for even longer than those who imagined good deeds.