Exercise scientists reported that even a 20-minute reduction in sedentary time on Saturdays and Sundays added up to a loss of more than 2 pounds and 1.6 percent of body fat after a year. But the same association was not seen with sedentary time during the weekdays.
"We know that, on average, people consume less or eat healthier diets on weekdays," explained study author Clemens Drenowatz, an assistant professor of exercise science at University of South Carolina in Columbia, S.C.
"So, they may be able to get by with less activity on weekdays because their diet makes up for it. On weekends, they're eating more, which requires more activity or less sedentary behavior to offset," Drenowatz said.
The study findings were scheduled to be presented Wednesday at an American Heart Association meeting in Phoenix. Studies presented at scientific conferences typically have not been peer-reviewed or published, and results are considered preliminary.
Much research in recent years has established an association between sedentary behavior -- which includes time sitting watching television or using computers -- with poor health outcomes, such as heart disease, diabetes, obesity and some cancers, according to the American College of Sports Medicine.
In a group of 332 adults ages 20 to 35, Drenowatz and his colleagues measured the time participants were sedentary by using a device that measured inactivity over a 10-day period. Participants also reported their own sedentary behaviors separately for weekdays and the weekend.
In addition, the study participants' body weight and body fat measurements were taken every three months over a one-year period.
"From what we saw, the overall sedentary time wasn't different on weekdays versus weekends," Drenowatz said. "A lot of people had sedentary occupations, like office jobs, and they didn't really make up for that on the weekends either. This suggests diet is the reason, though obviously more research needs to be done."
Two clinicians from Christiana Care Health System in Wilmington, Del., weighed in on the findings. They suggested that healthy workplace behaviors -- such as light lunches and midday walks -- may help balance out the negative effects of sitting at a desk all day.
Many people "don't really have the option of being that inactive on weekdays," said Dr. Omar Khan, medical director for community health at Christiana Care. "Weekends are a whole different matter. There's a big opportunity to be healthy -- or, as many of us tend to be, fairly unhealthy. With a two-day chunk of potentially being a couch potato, anything we do in that space can be fairly significant."
Karen Anthony, senior program manager for community health at Christiana Care, suggested that moving around for an extra 20 minutes on the weekends -- which seemed to spur measurable weight loss in study participants -- could lead to even more activity.
"Twenty minutes is a fraction of your weekend," she said. "It doesn't take a whole lot of extra movement to see that result."
Drenowatz said it's important to distinguish between exercising and merely reducing sedentary time, which means less sitting.
"I'm not telling people they need to go out and exercise -- that's a separate issue -- but just to reduce their sedentary time. It may be just standing up and walking around a bit ... can help," Drenowatz suggested.
He and Khan also noted that a loss of 1.6 percent of body fat over one year simply by moving 20 minutes more on the weekends may have a positive impact on the risks for developing heart disease.
"A lot of people get caught up with body weight, but from a health perspective, body fat and where it's located actually has a bigger impact on cardiovascular disease over the long term," Drenowatz said.
The American College of Sports Medicine offers tips on reducing sedentary behaviors.
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