Learn how simple tricks to improve your willpower can make it easier to stick to an exercise plan.

A rough day can drain your willpower, and make after-work workout plans harder to stick with.

RODALE NEWS, EMMAUS, PA—We all have days like this: You've got the motivation to lose weight and the desire to do so, but at the end of the day, you're just too tired to get yourself to the gym. Or are you? A new study published in the journal Psychology and Health suggests that exhaustion may have nothing to do with it. This study of Canadian college students found that a rough day can sap willpower. And that makes it too easy to succumb to the temptation to veg out on the couch rather than go for a run.

THE DETAILS: Researchers put 61 healthy but nonexercising college students through a series of mental and physical tests to see how sapping their self-control mentally would impact their desire to work out. For the first portion of the test, the students rode a stationary bike for 15 minutes while the researchers measured their level of exercise intensity. They were then asked to plan out their own exercise routine on some of the gym's equipment, and record the level of intensity at which they planned to do each exercise. At the third stage of the test, one group of students underwent a challenging mental task, while the other group was given something very simple to do. Finally, the students were asked to repeat the planning of an exercise routine, and then perform another 15-minute ride on the bike.

Compared with the group given the easy mental task, the students who were challenged performed the second bike ride at a much lower level of intensity than they did their first bike ride, and they planned out a second exercise routine that left them working out at much lower intensities than their first exercise routine.