According to the first nationwide study of physical fitness, more than one-third of U.S. teenagers and about 14% of young adults have low levels of cardiovascular fitness.
Citation to study: Carnethon, M.R., Gulati, M. Greenland, P. Prevalence and Cardiovascular Disease Correlates of Low Cardiorespiratory Fitness in Adolescents and Adults. JAMA. December 21, 2005;294 (23):2981-2988. Check COAST for availability.