Adolescence offers a unique opportunity for establishing positive health behaviors that can persist into adulthood. One such health behavior is engaging in increased levels of physical activity. During adolescence physical activity dramatically decreases, with children and teens demonstrating a 50 % reduction in their total daily expenditure of energy per body weight (Kemper, 2002). Decreased physical activity has been linked not only to obesity but also to depression and greater risk of hypertension and cardiovascular disease in adulthood (Lobstein, Baur, & Uauy, 2004). Increasing physical activity, in conjunction with appropriate dietary modifications, is a well-established means for controlling obesity (Hayman, 2002). Given the striking increase in prevalence of adolescent overweight and obesity, it is imperative that effective interventions are developed for the adolescent population.

From the 1980s to the early 2000s, the prevalence of obesity (defined as a body mass index at least in the 95th percentile, CDC, 2004) among adolescents has increased dramatically. According to a 2003–2004 Centers for Disease Control and Prevention (CDC) survey, the prevalence of obesity increased from 11 % to 19 % among 6- to 11-year-olds and increased from 11 % to 17 % among 12- to 19-year-olds (CDC, 2004). These recent increases have been particularly evident among non-Hispanic black and Mexican-American adolescents (Zametkin, Zoon, Klein, & Munson, 2003). The current estimates of adolescent obesity in the United States suggest the presence of racial disparities, with 21.5 % of African-Americans, 21.8 % of Hispanics, and 12.3 % of non-Hispanic whites being overweight (Strauss & Pollack, 2001). The CDC has labeled these increases in obesity prevalence as an epidemic that is linked not only to the overconsumption of foods but also to sedentary lifestyle behaviors (Clemmens & Hayman, 2004).

Childhood and adolescent obesity can have physical, psychological, and social consequences and can contribute to future complications in adulthood. For example, type 2 diabetes, which was formerly thought of as an adult disease, is now becoming more prevalent among children and adolescents (Baranowski et al., 2000). Childhood- and adolescent-onset obesity may be associated with higher rates of death and cardiovascular mortality than adult-onset obesity. Adults who were obese as children have been found to have increased morbidity and mortality regardless of adult weight (Riddoch, 1998; Styne, 2001). Obesity increases the risk of cardiovascular disease, insulin resistance, diabetes, hypertension, cancer, gall bladder disease, and atherosclerosis (Styne, 2001). There are psychological ramifications of obesity as well. It has been found that obese children as young as 5 years old report feeling decreased self-esteem due to their obesity (Bradford, 2009). Furthermore, nearly half of obese adolescents report moderate to severe depressive symptoms and a third report feelings of anxiety (Bradford, 2009).

Traditionally, overweight and obesity have been framed in a biopsychosocial framework in which genetic and biologic, psychological, and environmental factors overlap. It has been estimated that genetic factors contribute to a third of obesity (Bradford, 2009). These genetic factors include the hundreds of genes and genetic markers that have been linked to obesity, family syndromes, such as hyperinsulinism, and the genetic influence on energy expenditure and eating behaviors (Bradford, 2009). Biologic factors can include endocrine disorders such as hypothyroidism, medications, and medical treatments. Although there are many associations between obesity and psychological diagnoses, the causal relationships are unclear. Environmental factors include parental obesity, sedentary lifestyles, eating habits, and sleep deprivation. Because of the relatively short time period in which this increase in obesity has occurred, it cannot be explained solely by genetic factors (Ferreira et al., 2006). It is more likely that behavioral and environmental factors play a greater role in the obesity epidemic.

One such behavioral factor is the recent increase in adolescent inactivity. Adolescents spent 75.5 % of their day inactive, with an average of 5.2 (SD  =  1.8) hours spent engaging in television, computer, and homework activities (Strauss, Rodzilsky, Burack, & Colin, 2001). Only 1.4 % of an adolescent’s day is spent engaging in vigorous activity (Strauss et al., 2001). This amounts to 10 hours of sedentary behavior per day with only 12–13 minutes of physical activity per day. Strauss and colleagues’ findings are in sharp contrast with the international guidelines for physical activity that recommend engaging in at least an hour of physical activity on a daily basis (Biddle, Sallis, & Cavill, 1998). These activities should occur in the context of family, school, and community activities and should be enjoyable, engage a variety of muscle groups, and include weight-bearing activities (Sallis & Patrick, 1994). The Youth Risk Behavior Surveillance System estimated that 45.6 % of boys and 27.7 % of girls are meeting these guidelines (Camacho-Minano, LaVoi, & Barr-Anderson, 2011).

Aside from managing overweight and obesity, there are many other physical, psychological, and social benefits of physical activity for adolescents. There is a consistent positive relationship between physical activity and overall mental well-being (Hallal, Victora, Azevado, & Wells, 2006; Mutrie & Parfitt, 1998). Psychological benefits of physical activity for adolescents include reduction of tension and anxiety, reduction in feelings of depression, strengthening of stress coping skills, improvement in concentration and memory, improvement in positive self-image and self-confidence, and improvement in sleeping patterns (Heaven, 1996, p. 153). A recent review found that adolescent exercise resulted in positive effects on self-esteem (Hallal et al., 2006). It was also found that exercise reduced need for thinness, changes in body composition, and frequency of bingeing, purging, and laxative abuse among bulimic adolescent and young adult females (Hallal et al., 2006).

Physical activity also has positive impacts on adolescent social health. Social advantages of physical activity include games and organized sports that provide opportunities to work with others on a team, interact with others, and develop social skills (Heaven, 1996, p. 153). Participating in school and community activities is associated with short- and long-term indicators of positive development (Barber, Stone, & Eccles, 2005). Furthermore, it has been found that athletic youth are more likely to have opportunities to play sports, make friendships, and be part of an in-group (Pender & Stein, 2002). These athletic activities provide a space for social development (Barber et al., 2005). Physical activities can serve to structure an adolescent’s peer group: adolescents involved in extracurricular activities tend to have more academic friends and fewer friends who skip school and use drugs (Barber et al., 2005). Finally, in a study, participation in team sports was found to be linked to better academic outcomes as well as adult educational attainment, occupation, and income (Barber et al., 2005).

The research on the physiological benefits of physical activity has primarily focused on cardiovascular disease, skeletal health, and lung capacity. Because of the relatively low prevalence of morbidity and mortality related to cardiovascular disease in the adolescent population, most research investigating the relationship between physical activity and cardiovascular disease among adolescents has focused on cardiovascular risk factors (Twisk, 2001). Physical activity has been found to have a beneficial effect on high-density lipoprotein (HDL) cholesterol, body fatness, and cardiopulmonary fitness (Twisk, 2001) as well as aid in a range of factors associated with metabolic syndromes overall (hypertension, obesity, insulin resistance, impaired lipid and lipoprotein profile) (Hayman, 2002).

Knowledge regarding the long-term effects of exercise on skeletal health is incomplete; however, research suggests that vigorous physical activity may help to enhance bone mineral density in children. Furthermore, immobility and inactivity are associated with negative effects on skeletal health. Overall, it appears that low-impact activity, even without vigorous physical activity, is associated with better skeletal health (Riddoch, 1998). In a review by Hallal et al. (2006), the positive skeletal and bone density effects attained via adolescent physical activity were found to have a long-term protective effect on skeletal health in adulthood. There also appeared to be long-term positive effects for preventing breast cancer. Physical activity has also been found to significantly increase lung functioning among cystic fibrosis patients and certain types of physical exercise (e.g., swimming) in adolescence have been found to reduce the severity of asthma symptoms (Hallal et al., 2006).

Several large-scale studies have shown that physical inactivity in adolescence results in cardiovascular disease indirectly via the mechanisms that relate to beneficial effects of physical activities on blood pressure and serum lipoprotein profiles (Berlin & Colditz, 1990; Powell et al., 1987). Physical inactivity is a direct and indirect risk factor for adult diseases including cardiovascular diseases, cancer, and other chronic diseases. Atherosclerotic processes begin early in life, and it is possible that a sufficient amount and intensity of exercise during adolescence could decelerate this process. In a prospective study, it was found that being overweight during adolescence predicted a broad range of adverse health problems in adulthood independent of being overweight in adulthood (Riddoch, 1998). Obesity, cardiovascular problems, osteoporosis, and some kinds of cancer which are related to sedentariness in adults have also been found to originate in childhood (De Bourdeaudhuij, 1998).

Health behavior patterns established during adolescence affect the quality of life during adolescence and serve as the foundation for health-related lifestyles in adulthood (Pender & Stein, 2002). The specific goal of exercise promotion among children is to establish healthy exercise habits that will continue throughout life and subsequently improve current and future health outcomes (Riddoch, 1998).

Although research has not found direct negative effects of physical activity on mental health, there is some concern that involvement in certain sports may increase the risk of some girls developing eating disorders. This is highlighted by the finding that 20 % of female athletes in Norway were defined as at risk of an eating disorder (Mutrie & Parfitt, 1998). Although it is unclear how being involved in athletics may be linked to eating disordered behavior, it is interesting that such a significant percentage of females with eating disorders are involved in athletics. There is some evidence that physical activity can have adverse effects on adolescent physical health. Epidemiological data has revealed that sports injury is the leading cause of physical injury among adolescents (Emery, 2003). Strenuous physical activity has been found to adversely affect the female reproductive system resulting in athletic amenorrhea and weight lifting during adolescence could lead to musculoskeletal injuries and interrupt growth (Hallal et al., 2006). It is possible that growing trends toward sports-related injuries among adolescents are associated with increased intensity of training, competition, skill, and duration of sports at increasingly younger ages (Emery, 2003).

Adolescents may be at risk for sports-related injuries due to improper technique, ill-fitting protective equipment, training errors, muscle weakness, and imbalance (Cassas & Cassettari-Wayhs, 2006). In a review by Emery (2005), the author revealed a number of non-modifiable and potentially modifiable risk factors that were found to be correlated with increased rates of injury. These risk factors included previous injury, older age, male gender, higher contact sports, higher level of skill, position played, weather, fitness level, training, flexibility, strength, joint stability, balance and proprioception, and psychological or social factors (Emery, 2005).

It is likely that knowledge regarding these risk factors will aid in efforts to prevent adolescent injury. In a review by Abernethy and Bleakley (2007), the authors found mixed results for protective equipment as a means of preventing sports-related injury. It appears that the use of headgear is related to an increased rate of head injury with little evidence supporting the use of mouth guards as a protective strategy. The authors also found little evidence supporting bracing methods with an increased rate of injury associated with the use of protective external bracing. They did find some evidence for the use of knee pads in reducing lower limb injury. Finally, the authors did find support for conditioning programs that included strength, flexibility, and technique training programs occurring both preseason and during the sport-specific season. The authors note that there was no evidence for programs that focused on stretching alone.

Although most adolescent injuries occur in sports contexts, there appears to be less support for adolescent injuries incurred in supervised physical education and after-school environments. In a review by Strong et al. (2005), the rate of injury in both settings was nearly zero. Overall, it appears that although there is some risk of injury when adolescents are involved in competitive sports, it appears that these risks are outweighed by the potential benefits of physical activity.

It is clear that there are many benefits of engaging in physical activity (Biddle et al., 1998; Hayman, 2002; Hallal et al., 2006; Mutrie & Parfitt, 1998; Twisk, 2001). For these reasons, guidelines have been established regarding optimal levels of adolescent physical exercise. The International Consensus Conference on Physical Activity Guidelines for Adolescents was convened in the 1990s and recommended that all adolescents should engage in physical activity daily or nearly every day, and adolescents should engage in moderate to vigorous levels of physical activity at least three times a week for at least 20 minutes (Sallis & Patrick, 1994).