Leisure-Time Physical Activity, Sedentary Behavior, and Physical Fitness among Adolescents: Varying Definitions Yield Differing Results in Fitness Research
Kerner, Matthew S., JOPERD--The Journal of Physical Education, Recreation & Dance
A number of relationships involving physical activity and health are well-documented in the literature. Physical inactivity is associated with overweight and weight gain (Tremblay et al., 1990; Williamson et al., 1993) and with relative risk for coronary heart disease, the leading cause of death in North America (Sallis, Patterson, Buono, & Nader, 1988; Sandvik et al., 1993). Obesity among young children and adolescents has increased in the past 20+ years, with the rates of obesity ranging between six and 33 percent (Dietz, 1986; Kerner et al., 2001; Troiano, Flegal, Kuczmarski, Campbell, & Johnson, 1995). Additionally, childhood physical inactivity may exacerbate other behaviorally linked risk factors, such as hypertension and hyperlipidemia. Coronary artery disease risk factors in children have been associated with subsequent morbidity and mortality later in life (Sandvik et al., 1993). Evidence suggests that physical activity during childhood and adolescence can facilitate optimal growth and development (Cooper, 2001) and that adult physical activity is related to exercise patterns established in childhood (Cooper, 2001; U.S. Department of Health and Human Services, 1996).
Computers and the Internet have become integrated into our lives and incorporated into the delivery of education and leisure. In a population of ninth-grade African American girls, Internet use was reported to average over nine hours per week (Kerner et al., 2001). This mode of leisure-time activity appears to contribute to the same hypokinetic behavior as television watching, which is speculated to be a modifiable cause of obesity (Anderson, Crespo, Bartlett, Cheskin, & Pratt, 1998).
While the relationship between television watching and physical activity has frequently been studied, the same cannot be said about the relationships among Internet use, physical activity, and physical fitness. Investigating these relationships is Important because of the apparent hypokinetic nature of Internet use and the hypothesized relationships between physical fitness, physical inactivity, and relative risk for coronary heart disease.
Kerner, Kurrant, and Kalinski (2004) sought to compare television-watching time and Internet-use time to three different operational definitions of leisure-time physical activity. Previous studies have found no significant relationship between sedentary behavior and leisure-time physical activity in similar-age populations (Anderson et al., 1998; Kerner et al., 2001; Robinson & Killen, 1995). This is somewhat surprising since logic dictates that the more leisure time expended being sedentary, the less leisure time is available for physical activity. In a six-month interventional study designed to reduce television watching in a population of third- and fourth-grade school children (Robinson & Killen, 1995), significant reduction in body mass index (BMI), triceps skinfold thickness, waist circumference, and waist-to-hip ratio occurred in the intervention group relative to controls. Nonetheless, other outcome measures--such as time spent in moderate-to-vigorous physical activity and cardiorespiratory fitness measured by a 20-meter shuttle-run--failed to change. As Marshall and coworkers concluded (Marshall et al., 2002), "Physical activity and sedentary behavior are not two sides of the same coin" (p. 415).
Kerner et al. (2004) also endeavored to appraise the relationship between leisure-time physical activity and two essentially different gauges of physical fitness, one more health related (i.e., BMI, sum of skinfold thicknesses, percent body fat), the other more performance related (mile-run time).
Physical fitness is a graded, independent, long-term predictor of mortality from cardiovascular causes in healthy, middle-aged men (Sandvik et al., 1993). In another study (Lakka et al., 1994), higher levels of cardiovascular fitness had a strong, graded, inverse association with the risk of acute myocardial infarction, supporting the idea that lower levels of cardiovascular fitness are an independent risk factor for coronary heart disease. …