A common reason for not exercising is work-related fatigue — a rationale that has puzzled exercise physiologists and health professionals because of the generally low caloric demands of many job settings.

A new study explains the work-related fatigue as researchers discover if you use your willpower to do one task, it depletes you of the willpower to do an entirely different task.

However, strategies can be used to call up the resolve to exercise.

Interestingly, after the exercise session the fatigue often abates, perhaps as a function of endorphin release or some other mechanism with the individual feeling refreshed and invigorated.

“Cognitive tasks, as well as emotional tasks such as regulating your emotions, can deplete your self-regulatory capacity to exercise,” says Kathleen Martin Ginis, associate professor of kinesiology at McMaster University, and lead author of the study.

Martin Ginis and her colleague Steven Bray used a Stroop test to deplete the self-regulatory capacity of volunteers in the study. (A Stroop test consists of words associated with colors but printed in a different color. For example, “red” is printed in blue ink.) Subjects were asked to say the color on the screen, trying to resist the temptation to blurt out the printed word instead of the color 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.”

Still, she doesn’t see that as an excuse to let people loaf on the sofa.

“There are strategies to help people rejuvenate after their self-regulation is depleted,” she says.

“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 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 says.

The study is published in the journal Psychology and Health.

Source: McMaster University