At more than 220 pounds, Christina Martinez knew her lifestyle had to change dramatically if she wanted to improve her health, so she started taking aerobics classes.

A rigorous, five-days-a-week workout routine helped her drop 42 pounds and lower her blood pressure to the point she no longer had to take medication, she said.

"I was worried and scared," said Martinez, 49, a mother of three who lives in Chicago's Pilsen neighborhood. "Healthwise, that was my first concern. Then, it was my weight."

A recently released national report by the U.S. Centers for Disease Control and Prevention that surveyed inactivity and obesity rates on a county-by-county basis underscores the need for more Americans to follow Martinez's get-it-done example.

The survey found that in 2008 an estimated 25.4 percent of U.S. adults were affirmed couch potatoes, spending none of their free time engaged in such physical activities as walking, gardening or running.

Overall, the seven Chicago-area counties were slightly more active than the national average, with DuPage County harboring the lowest percentage of couch potatoes, an estimated 18 percent, and Kendall County the highest, at 24 percent. In Cook County, an estimated 23 percent of adults were inactive.

Martinez was not always inactive. In fact, she had a gym membership until she became pregnant with her second child.

"I stopped going because I thought it wasn't good for the baby," said Martinez, who six years ago was told by a doctor that she had high blood pressure and needed to start exercising to manage it.

For Martinez, as for many other Americans, all that inactivity added up at the scale.

The CDC's corresponding county-by-county look at obesity found that an estimated one-third of adults are obese, based on their body mass indexes. Calculated using a person's weight and height, the BMI provides a rough estimate of body fat.

The CDC reports that about 1 in 4 adults in Cook County were obese in 2008, up about 4 percentage points from 2004. In other area counties, the obesity rates ranged from about 24 percent in DuPage and Lake to nearly 29 percent in Will.

The data offer local public health officials the most detailed look to date at the prevalence of inactivity and obesity, which can lead to deadly chronic illnesses such as Type 2 diabetes and heart disease, the CDC reports.

"These findings help states and localities identify their most serious or pressing public health problems," said Karen Hunter, a CDC spokeswoman.

What the data do not highlight is the striking prevalence of obesity in some pockets of the Chicago area, particularly in black and Hispanic neighborhoods, experts say.

"A global number like (the CDC estimates) can tell you basic regional information," said Amy Luke, nutritional epidemiologist in the department of preventive medicine and epidemiology at Loyola University's Stritch School of Medicine. "Certainly, anyone in the public health field understands that this is really an overall figure and that clearly there are subpopulations that require additional assistance."

Take Maywood.

More than half of adults between 25 and 45 in the predominantly blue-collar African-American suburb are obese, said Luke, citing preliminary data collected last year from a sample of 280 adults in the Maywood area.

Loyola researchers have been looking closely at obesity in the Maywood area as part of a global study on how diet and exercise affect body weight. Luke stressed that the sample of participants is not random but added the findings are relatively representative of the age group and ethnicity.

The researchers at Loyola are also finding that processed food, fast food and entrees that consist mostly of red meat are a big part of the diets of their Maywood subjects.