Progress and future directions on physical activity research among youth.

There is strong evidence to support the benefits of regular physical activity for children and adolescents (heretofore referred to as "youth"). Evidence includes improved cardiorespiratory fitness, muscular fitness, bone health, body composition, and cardiovascular and metabolic health biomarkers. Importantly, physical inactivity is a modifiable risk factor for lifestyle-related chronic diseases and conditions and may track through adulthood. Because of the potential benefits and modifiable nature of the behavior, the "2008 Physical Activity Guidelines for Americans" recommends 1 hour or more of daily physical activity for youth. Most of the time should be spent in either moderate-or vigorous-intensity aerobic activities and should also include muscle and bone strengthening activities. The 2010 World Health Organization "Global Recommendations for Physical Activity and Health" supports similar guidelines for youth.