Washington : The motivation to exercise fluctuates from week to week, which can tell whether people will be physically active or not, suggests a report.

"Many of us set New Year resolutions; to be more physically active, and we expect these resolutions to be stable throughout the year," said David Conroy, professor of kinesiology at Penn State University.

Conroy and his colleagues recruited a group of college students and assessed them over a period of 10-weeks, both the students' weekly intentions to be physically active and their activity levels, according to a Penn statement.

According to the report, during each of the 10 weeks, participants were instructed to log on web-site to rate their intentions to perform physical activity for the week ahead.Participants were also instructed to wear pedometers each day for the first four weeks to assess physical activity.

"Our motivation to be physically active changes on a weekly basis because we have so many demands on our time. Maybe one week we're sick or we have a work deadline or in the case of students, an upcoming examinations can be reason. But these lapses in motivation really seem to be destructive," Conroy said, who conducted the study, the Journal of Sports and Exercise Psychology reports.

The team found that, in many participants the motivation to exercise fluctuated on a weekly basis, and these fluctuations were linked to their behaviour.

"One of the things we found in this study is that from week to week our motivation level can change a lot, and these weekly changes in motivation can be destructive to our resolutions," said Conroy.

"Our results suggest that people with consistently strong intentions to exercise have the best chance of actually following through on their intentions," Conroy adds.