1. Prevalence of no leisure-time physical activity - 35 states and the District of Columbia, 1988-2002;Centers for Disease Control and Prevention;Morb Mortal Wkly Rep,2004
2. Public Health Agency of Canada Physical activity tips for adults (18-64 years) 2012 http://www.phac-aspc.gc.ca/hp-ps/hl-mvs/pa-ap/07paap-eng.php
3. Statistics Canada Canadian Health Measures Survey: physical activity of youths and adults 2011 http://www.statcan.gc.ca/daily-quotidien/110119/dq110119b-eng.htm
4. Association between physical activity and mental disorders among adults in the United States;Goodwin;Prev Med,2003