Story highlights The American College of Sports Medicine releases its American Fitness Index report

Washington is the "Nation's Fittest City"; Indianapolis ranks last

Experts say a city's infrastructure and variety of outdoor activity options affect the health of its residents

(CNN) Regardless of where you live in the United States, one trend seems to be clear: The more pedestrian-friendly the city, the healthier its residents, according to a recent report released by the American College of Sports Medicine.

For the eighth year running, the American Fitness Index report has provided a snapshot of health and fitness across 50 cities, and the nation's capital has topped the list a second year in a row as the "Nation's Fittest City." Minneapolis-St. Paul and San Diego were strong contenders, rounding out the top three spots. Indianapolis, known for its car racing, finished last in the heat, as the nation's least fit city, with Memphis and Oklahoma City close behind.

Leading experts in the field of sports medicine and exercise science say personal and environmental factors contribute to the rankings.

"The American Fitness Index is two things: a measure of how healthy a metro area is today, and a call to action for urban and suburban leaders to design infrastructures that promote active lifestyles and lead to positive health outcomes," said Walter R. Thompson, chairman of the American Fitness Index Advisory Board and professor of kinesiology and heath at Georgia State University. "Our goal is to provide communities and residents with resources that help them assess, respond and achieve a better, healthier life."

Cities continuously use the data provided by the American Fitness Index report to make changes in their policies and urban planning. St. Louis had one of the biggest gains this year, jumping from No. 41 on the list in 2014 to No. 30, and much of its success has been attributed to an increase in residential recreational facilities, city parks and farmers' markets, study experts say. Oklahoma City, which ranked last in 2012, improved this year after the mayor launched a " This City is Going on a Diet " campaign, in which residents reached a goal of losing a collective 1 million pounds last month.

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