According to the Boulder, Colo.-based Leisure Trends Group, the average adult American has about 35 hours of leisure time available each week — an average of four hours per weekday and seven hours per weekend day.

Even with the limited time available for leisure and recreation, two-thirds of Americans engage in at least one core human-powered outdoor recreational activity annually. The outdoor recreation population has grown larger, younger and more dedicated over a six-year study period, according to the 2004 Outdoor Recreation Participation Study for the United States, released in August by the Outdoor Industry Association.

The study's analysis of outdoor recreation behavior in 21 human-powered activities performed by Americans age 16 and over found 16 million new faces added to the rolls of casual or devoted outdoor participants since 1998 — outpacing natural population growth by a healthy margin. According to the study, the bulk of both casual and devoted participants are centered on the cornerstone activities of bicycling, hiking and camping. Known as gateway activities, these pursuits are the primary anchor for attracting new participants and provide an affordable non-intimidating entry point to other outdoor activities.