Is TV viewing an index of physical activity and fitness in overweight and normal weight children?
To assess relationships between TV viewing and body composition, energy expenditure, physical activity, fitness and nutrition habits in prepubertal children. Cross-sectional study. Sixty prepubertal children (mean body mass index: 20.8 kg m(-2), age: 5-11 years, overweight: n = 52, normal weight: n = 8). TV consumption, socio-economic status (SES) and nutrition habits were estimated by questionnaires. Fat mass and fat-free mass were assessed by anthropometrics and bioelectrical impedance analysis, and resting energy expenditure by indirect calorimetry. Total energy expenditure was measured by a combination of indirect calorimetry and individually calibrated 24-hour heart rate (HR) monitoring. Activity-related energy expenditure and physical activity level were calculated. Aerobic fitness (VO2 submax) was determined by ergometry, muscle strength (musculus quadriceps, musculus ischiocruralis) was measured by computer tensiometry. Children were stratified according to their daily TV consumption: <or=1 h of TV per day (group I) and >1 h of TV per day (group II). When compared with children of group I, children of group II had increased body weight, body mass index, skinfolds, fat mass and prevalence of overweight (P < 0.05 and <0.01, respectively). By contrast, fat-free mass, energy expenditure, measures of physical activity and muscle strength were similar. Children of group II had normal absolute VO2 submax but reduced adjusted VO2 submax (P < 0.05). They also had parents with a lower educational level (P < 0.05). Similar nutritional habits were observed in both groups. There were no significant differences in the observed parameters between children with high (1-3 h day(-1)) and very high (>3 h day(-1)) TV viewing. There is a positive relationship between TV viewing and fatness. Increased TV viewing does not reflect reduced 24-hour energy expenditure as assessed by 24-hour HR monitoring, submaximal VO2, muscle strength or poor dietary intake. Increased TV consumption is associated with a low SES.