"You don't have to be the fittest person who is exercising every day to receive the feel-good benefits of exercise," said David Conroy, professor of kinesiology. "It's a matter of taking it one day at a time, of trying to get your activity in, and then there's this feel-good reward afterwards."

Conroy added that it often is hard for people to commit to an exercise program because they tend to set longterm rather than short-term goals.

"When people set New Year's resolutions, they set them up to include the entire upcoming year, but that can be really overwhelming," he said. "Taking it one day at a time and savoring that feel-good effect at the end of the day might be one step to break it down and get those daily rewards for activity. Doing this could help people be a little more encouraged to stay active and keep up the program they started."

The researchers asked 190 university students to keep daily diaries of their lived experiences, including free-time physical activity and sleep quantity and quality, as well as their mental states, including perceived stress and feeling states. Participants were instructed to record only those episodes of physical activity that occurred for at least 15 minutes and to note whether the physical activity was mild, moderate or vigorous. Participants returned their diaries to the researchers at the end of each day for a total of eight days. The researchers published their results in the current issue of the Journal of Sport and Exercise Psychology.

According to Amanda Hyde, kinesiology graduate student, the team separated the participants' feeling states into four categories: pleasant-activated feelings exemplified by excitement and enthusiasm, pleasant-deactivated feelings exemplified by satisfaction and relaxation, unpleasant-activated feelings exemplified by anxiety and anger, and unpleasant-deactivated feelings exemplified by depression and sadness.

"We found that people who are more physically active have more pleasant-activated feelings than people who are less active, and we also found that people have more pleasant-activated feelings on days when they are more physically active than usual," said Hyde, who noted that the team was able to rule out alternative explanations for the pleasant-activated feelings, such as quality of sleep.

"Our results suggest that not only are there chronic benefits of physical activity, but there are discrete benefits as well. Doing more exercise than you typically do can give you a burst of pleasant-activated feelings. So today, if you want a boost, go do some moderate-to-vigorous intensity exercise."

Conroy added that most previous studies have looked only at pleasant or unpleasant feelings and paid less attention to the notion of activation.

"Knowing that moderate and vigorous physical activity generates a pleasant-activated feeling, rather than just a pleasant feeling, might help to explain why physical activity is so much more effective for treating depression rather than anxiety," he said. "People dealing with anxious symptoms don't need an increase in activation. If anything, they might want to bring it down some. In the future, we plan to look more closely at the effects of physical activity on mental health symptoms."

Other authors on the paper include Aaron Pincus, professor of psychology, and Nilam Ram, assistant professor of human development and family studies and of psychology.

National Institute on Aging and the Penn State Social Science Research Institute funded this research.

Journal Reference:

1. David E. Conroy, Steriani Elavsky, Amanda L. Hyde, and Shawna E. Doerksen. The Dynamic Nature of Physical Activity Intentions: A Within-Person Perspective on Intention-Behavior Mechanism Sheds Light On How the Brain Adapts to Stress