ANN ARBOR—Exercising to lose weight? Think of another reason or the odds are you won’t be exercising for long, according to a University of Michigan study of baby boomer women.

The study, reported in the journal Sex Roles, found that women who exercise for a body shape motive, such as wanting to lose weight or to become toned, spend about 40 percent less time exercising than women who exercise for motives not related to achieving a certain body shape or weight.

“Everyone knows that exercise is good for them. Most don’t do it consistently,” said Michelle Segar, a U-M psychology researcher who collaborated with Susan Nolen-Hoeksema, former U-M psychology professor, and Donna Spruijt-Metz of the Institute of Health Promotion and Disease Prevention in Los Angeles.

Researchers say there appears to be a greater chance of maintaining exercise habits when the exercise is for a non-body shape reason, such as reducing stress, increasing a sense of well-being, or for the intrinsic enjoyment of the activity itself for social reasons, such as wanting to do something with a friend.

The women studied, all in their mid-40s, reported how much they exercised in a typical week. Nearly half” 44 percent” said they exercised to lose weight, maintain weight and/or tone their bodies, and these women did almost 40 percent less exercise than others with non-body shape motivation.

Research shows that the reasons people initiate exercise regimes are different from the reasons associated with participating long term. Intrinsic reasons, such as enjoying the physical activity you participate in, are considered important for maintaining the activity over time.

In contrast, women who decide to exercise to lose weight or change their body shape may select physical activities based on how many calories they burn, rather than on how much they will like doing that activity” a recipe for eventually quitting.

“We’re all so busy. Who has time to fit in an activity you don’t really enjoy?” Segar said.” Don’t take up running if you don’t particularly enjoy running. You’re better off to find something more pleasurable, like walking with a friend, or to do something you do like and will keep doing long-term as a regular part of your life.”

The study also found:

“Women exercising with a body-shape motivation reported walking 2