Willpower is a muscle: Use it or lose it

You resisted yelling at your son when he refused to eat his breakfast. You avoided checking Facebook on your BlackBerry during a board meeting. And you opted for an apple instead of a chocolate bar at lunch. You may not be physically tired at the end of the day, but you just don't feel like working out.

A new study published yesterday in Psychology & Health suggests it may be because you've used up all your willpower.

Researchers from McMaster University in Hamilton found doing one task that depletes your self-control can make it difficult to sum up the willpower to do another - such as exercise.

A group of 61 study participants between the ages of 18 and 30 were asked to ride a stationary bike and researchers measured how much energy they exerted. They later asked 31 of the participants to ride the bike again, but first administered a Stroop test - in which participants had to read a list of colours (such as "red") that were printed in a different colour (such as blue ink). The participants who did the test exerted less energy in the bike ride the second time around than the 30 members of the control group did.

Researchers also found that participants who had done the willpower-busting Stroop test were more likely to skip workouts they had previously scheduled.

Doing the dishes or avoiding biting your nails may require a lot of willpower, but that shouldn't be an excuse not to work out, said Kathleen Martin Ginis, an associate professor of kinesiology at McMaster and lead author of the study.

She said if you plan a regular exercise routine and don't have to think about details such as duration, you're more likely to follow through.

You can also build up willpower by regularly challenging yourself to tasks that test your self-control.

"[Willpower]is like a muscle - the more you use it, the stronger it gets," Dr. Martin Ginis said. "Try to resist having that extra piece of cake."

And if you still don't feel like exercising, try listening to your favourite song or watching a video of kittens on YouTube.

"People in good moods have more willpower," she said.