On average, the women wore the straps for nearly 14 hours out of the 15-hour daytime period (defined as 7 a.m. to 10 p.m.). This allowed the team to assess total time spent engaged in daily light, moderate or vigorous physical activity.
Body composition assessments were conducted just before the accelerometer monitoring began and again 20 months later. In turn, after the 20-month re-assessment, the women were again asked to wear the accelerometers for another week of activity monitoring.
The result: Among the obese participants, physical activity was found to drop by 8 percent overall over the course of the 20-month study period. This was equivalent to a loss of 28 active minutes per week, the researchers said.
Non-obese women, on the other hand, showed no drop in their physical activity routines.
"This finding," Tucker said, "highlights the importance of maintaining an active lifestyle and a healthy weight in order to prevent the start of this potential cycle of increasing risks."
Lona Sandon, a registered dietitian and assistant professor of clinical nutrition at the University of Texas Southwestern in Dallas, said the viciousness of this cycle means this is often easier said than done.
"What we do know is that obesity is clearly related to more sedentary behavior," Sandon said. "But is it that they move less and become obese, or because they're obese that they move less?"
Sandon said there are many reasons an obese woman would stop being active.
"Certainly, when you become obese it's just harder to move your body, and you become winded or easily fatigued with very little activity," she said. "S you would just plain avoid it for that reason."
Psychological issues also come into play, Sandon said.
"Being obese gets tied to emotion and body image. You don't want people watching you. You don't feel comfortable going to a gym or a fitness class because people may be staring," she said. "Low self-esteem, poor body image and depression also oftentimes go along with obesity. There's a lack of confidence that they can lose the weight, and that in trying to do it they'll just bring unwanted attention to themselves."
The cycle of obesity and inactivity "is a very complicated and difficult situation," Sandon said.