If you do not feel like having the energy to go for a run after a rough day at the office, your limited willpower is to be blamed, says a new study.
Scientists say that if you use your willpower to do one task, it depletes you of the willpower to do an entirely different task.
"Cognitive tasks, as well as emotional tasks such as regulating your emotions, can deplete your self-regulatory capacity to exercise," said Kathleen Martin Ginis, associate professor of kinesiology at McMaster University, and lead author of the study.
The researchers used a Stroop test to deplete the self-regulatory capacity of volunteers in the study.
A Stroop test consists of words associated with colours but printed in a different colour. For example, "red" is printed in blue ink.
Subjects were asked to say the colour on the screen, trying to resist the temptation to blurt out the printed word instead of the colour itself.
"After we used this cognitive task to deplete participants' self-regulatory capacity, they didn't exercise as hard as participants who had not performed the task. The more people "dogged it" after the cognitive task, the more likely they were to skip their exercise sessions over the next 8 weeks. You only have so much willpower," she said
However, this, according to her could be no excuse for people to loaf on the sofa.
"There are strategies to help people rejuvenate after their self-regulation is depleted. Listening to music can help; and we also found that if you make specific plans to exercise-in other words, making a commitment to go for a walk at 7 p.m. every evening-then that had a high rate of success," she said.
She says that by constantly challenging yourself to resist a piece of chocolate cake, or to force yourself to study an extra half-hour each night, then you can actually increase your self-regulatory capacity.
"Willpower is like a muscle: it needs to be challenged to build itself," she said.
The study has been published in Psychology and Health.