Richard Alleyne, The Telegraph: Researchers found that "do-gooders" appear to be naturally stronger than their counterparts and that an act of heroism can actually improve your overall stamina.

The findings turn upside down the idea that being altruistic can be detrimental to your own advancement.

They also contradict suggestions that only those people with heightened willpower or self-control are capable of heroism.

Researchers believe that simply attempting heroic deeds can confer personal power.

"Gandhi or Mother Teresa may not have been born with extraordinary self-control, but perhaps came to possess it through trying to help others," said Kurt Gray, a psychologist at Harvard University.

He said people with strong willpower undergo a "moral transformation" which turns them from average to exceptional.

The team found that people with an evil streak do best when it comes to physical endurance but those who do good deeds can also receive a boost.

Psychologists claim extreme moral actions may increase people's capacity for willpower and physical endurance.

The research, which was published in the journal Social Psychological and Personality Science, involved two studies which compared moral behaviour and physical strength.

For the first, participants were given a dollar note and told either to keep it or to donate it to charity.

They were then asked to hold up a 5lbs weight for as long as they could. Those who donated to charity could hold the weight up for almost 10 seconds longer on average.

In a 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 did not benefit other people.

But those with a malicious streak were even stronger than those who imagined themselves doing good deeds.

Mr Gray said moral or immoral actions boosted people's ability when it comes to physical endurance.

He said: "People perceive those who do good and evil to have more willpower, and less sensitivity to discomfort.

"By perceiving themselves as good or evil, people embody these perceptions, actually becoming more capable of physical endurance."

Mr Gray said: "Whether you're saintly or nefarious, there seems to be power in moral events.

"People often look at others who do great or evil deeds and think, 'I could never do that' or 'I wouldn't have the strength to do that.' But in fact, this research suggests that physical strength may be an effect, not a cause, of moral acts."

Meanwhile a Newcastle University study published in the Royal Society journal Biology Letters found that giving to charity could be profitable in the long term.

They found that people were more likely to be co-operative and charitable to other people who themselves gave to charity.

Investing in a good reputation appears to be a strategic decision which can mean that helping others is self-interested in the longer term, it concluded.

It could also explain why altruism has not been eradicated by predominantly selfish evolutionary development.