ABC News' Dr. Seema Calip reports:

When it comes to exercise, Americans seem to be getting more of it. But obesity is still on the rise nearly everywhere in the country.

The new data comes from the Institute of Heath Metrics and Evaluation (IHME), which took a county-by-county look at self-reported physical activity levels and obesity rates across the United States. They found that, despite the fact that more Americans are at least saying they are getting more physical activity, nearly all U.S. counties registered a steady increase in obesity rates between 2001 and 2009.

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As far as why this might be happening, the authors of the report note that an active lifestyle may be just one piece of the obesity puzzle. Other factors - calorie-rich diets, for example, or a lack of community programs promoting or incentivizing healthy lifestyles - may make or break Americans' abilities to slow their slide into obesity.

Still, the findings on self-reported exercise - as well as some of the successes certain counties have had in slowing obesity rates locally - are promising, according to Dr. Christopher Murray, director of IHME and one of the report's lead authors.

"People have shown that they are able to make changes," Murray said. "There are communities that have had great success and we can learn from them."

Among these communities are Teton, Wyo., which in 2011 boasted the most active male population in the country. In all, 77.5 percent of the men there reported that they performed "sufficient physical activity" - a level defined as 150 total minutes of moderate activity or 75 minutes of vigorous activity per week. Routt, Colo., claimed the most active women, with 74.7 percent of them reporting sufficient physical activity.

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The biggest gains in self-reported physical activity levels were seen among counties in Kentucky, Georgia and Florida. The county with the highest increase for men was Concho County, Texas - up from 41.4 percent in 2001 to 58.2 percent in 2009. Meanwhile, women in Morgan County, Ky. saw the largest increase in physical activity - up from 25.7 percent in 2001 to 44 percent in 2009.

Yet the researchers found that obesity trends in all but nine counties were definitely on the rise - and even in these nine holdouts, they could not say for sure whether the obesity picture was actually improving or not, since the slight improvements they saw there did not reach what scientists call statistical significance.

Clearly, increasing physical activity alone is having a small impact on our nation's obesity levels, said Dr. Lou Aronne, director of the Comprehensive Weight Control Program at New York Presbyterian Hospital.

"There are several other factors to consider," he said. "One of the main ones being the availability of too much food."

In addition to diet, Aronne noted several other potential contributing factors - everything from lack of sleep to the effects of certain medications on weight gain. Even changes in the microorganisms in our intestines may play a part, he said.

"At an individual level, the energy balance is what is important and that boils down to increasing physical activity and reducing overall food intake."

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Whatever the reason, America's ballooning weight problem appears to be a crucial reason why - according to a separate report published Wednesday by Murray and his group in the Journal of the American Medical Association - the U.S. lags behind other wealthy nations in terms of improvements in life expectancy. This report identified increased body mass index as the third-leading risk factor contributing to years of healthy life lost in 2010.

Doctor's Take

Granted, though this research focuses a great deal on the cloud cast over the country's health in the form of obesity, the silver lining of increased physical activity is nothing to sneeze at. Those healthy steps that Americans appear to be taking off the couch could well be the first steps in turning the tide against obesity and improving the country's overall health.

What diet and nutrition experts are saying now is that we need to take a similar approach to the multitude of other factors that could be contributing to our waistlines - whether in our communities or at our kitchen tables.