It looks as if the West has won.

San Francisco is the fittest big city in the USA, just slightly more fit than Seattle, according to a scientific analysis of 16 cities released today by the American College of Sports Medicine at its annual meeting in Indianapolis.

But not all of the West is in top shape. Los Angeles is near the bottom of the list.

To rank big metropolitan areas, health and fitness experts analyzed government data from the 15 most populous cities in the country and Indianapolis, where the sports-medicine group is headquartered. They took into consideration a number of health indicators, including the percentage of people who exercise regularly, maintain a healthy weight, eat the recommended daily servings of fruits and vegetables, have access to health care, have health insurance and don't smoke. They also looked at the environment, including the availability of parks, walking/bike trails and public transportation.

This new analysis, called the American Fitness Index, is different from the rankings of fittest and fattest cities released annually by Men's Fitness, although some of the targeted health indicators are similar. For example, the magazine's editors examine such factors as time spent working out, average commuting time, the number of parks and time spent watching TV.

Government statistics show that about 66% of adults are overweight or obese, which increases their risk of type 2 diabetes, heart disease and some types of cancer. New data out Wednesday show that 32% of children and teens in the USA weigh too much.

"This epidemic of obesity is catching up with us, and one way we can combat it is to provide an environment where kids and families can exercise," says Walt Thompson, chairman of the panel that created the new index and a professor of exercise physiology at Georgia State University in Atlanta. His city came in No. 5, but he'd like to help Atlanta move up the list.

"We're targeting cities because that's where most people live, and they typically don't have the kind of environment that supports exercise, as opposed to somebody who lives out the country, where there is plenty of open space," he says. "Our hope is the cities on the bottom of the list will try to replicate some of the things that cities on the top of the list are doing."

Many cities already have initiatives to encourage more physical activity, but others need to be doing more, says Barbara Ainsworth, professor in the department of exercise and wellness at Arizona State University-Mesa. "Cities can take this information and use it to improve the quality of life for their residents."

The sports-medicine group's physical activity guidelines recommend that adult Americans, ages 18 to 65, do moderate-intensity aerobic activity (walking, dancing, biking) for at least 30 minutes five days each week and strength training at least twice a week for all their major muscle groups, including the chest, back, shoulders, upper legs, lower legs and arms. This could be strength training with free weights or machines or weight-bearing calisthenics such as pushups. It should be done on two non-consecutive days.

The aerobic activities should be done in at least 10-minute bouts, the group recommends. Short spurts of low-intensity movement — shopping, taking out the trash or walking a few minutes in the office or parking lot — don't count.

More information on the fit-city rankings is available at americanfitnessindex.org.