Background: According to the 2008 Physical Activity Guidelines for Americans, adults need to engage in at least 150 minutes/week of moderate-intensity activity or its equivalent (defined as aerobically active) to obtain substantial health benefits and more than 300 minutes/week (defined as highly active) to obtain more extensive health benefits. In addition to aerobic activity, the 2008 Guidelines recommend that adults participate in muscle-strengthening activities on 2 or more days/week. Purpose: This study examined the prevalence and trends of meeting the activity criteria defined by the 2008 Guidelines among U.S. adults. Methods: Prevalence and trends of participation in leisure-time physical activity were estimated from the 1998-2008 National Health Interview Survey (analyzed in 2010). Results: In 2008, 43.5% of U. S. adults were aerobically active, 28.4% were highly active, 21.9% met the muscle-strengthening guideline, and 18.2% both met the muscle-strengthening guideline and were aerobically active. The likelihood of meeting each of these four activity criteria was similar and were associated with being male, being younger, being non-Hispanic white, having higher levels of education, and having a lower BMI. Trends over time were also similar for each part of the 2008 Guidelines, with the prevalence of participation exhibiting a small but significant increase when comparing 1998 to 2008 (difference ranging from 2.4 to 4.2 percentage points). Conclusions: Little progress has been made during the past 10 years in increasing physical activity levels in the U. S. There is much room for improvement in achieving recommended levels of physical activity among Americans, particularly among relatively inactive subgroups. (Am J Prev Med 2010;39(4):305-313) Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine
