Each year, more than 170 million people visit national forests for recreation（娱乐，消遣） . And the physical activity associated with these visits burns 290 billion food calories. That equals enough french fries laid end to end to reach the Moon and back -- twice -- according to a recent study in the Journal of Forestry¹. While the recent strategic plan of the U.S. Forest Service includes sustaining and enhancing outdoor recreation opportunities, the benefits of exercise and outdoor recreation also are recognized by President Obama's America's Great Outdoors initiative to reconnect Americans with their landscapes, as well as the First Lady's Let's Move Outside campaign.

But how exactly do our national forests contribute to helping² people develop a healthier lifestyle? A recently published study may reveal some answers.

"We examined the extent that national forests might provide public health benefits by estimating the net energy expended³ for a range of outdoor activities engaged in by visitors to national forest lands," explains research forester Jeff Kline. "We did this by combining data describing national forest visitors' outdoor recreation activities with data characterizing the calories expended with each type of physical activity."

Kline, a scientist with the Forest Service's Pacific Northwest Research Station, and Oregon State University co-authors, Randall Rosenberger and Eric White, recently published their findings in the September issue of the Journal of Forestry. The article, "A National Assessment⁴ of Physical Activity in U.S. National Forests," contends（竞争，奋斗） that national forests can help Americans meet guidelines for regular physical activity set by the Centers for Disease Control and Prevention.

Key findings from the study include:
Hiking, walking, downhill skiing, fishing, relaxing, camping, relaxing, and driving for pleasure are among the primary activities accounting⁵ for about two-thirds (68 percent) of all visits to the national forests.
Annual energy expenditures⁶（能量消耗） in national forest recreation represent 6.8 million adults and almost 317,000 children meeting the Centers of Disease Control and
Prevention guidelines regarding regular aerobic⁷（需氧的） physical activity for a year.