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Objective: To assess relationships between TV viewing and body composition, energy expenditure, physical activity, fitness and nutrition habits in prepubertal children. Design: Cross-sectional study. Subjects: Sixty prepubertal children (mean body mass index: 20.8 kg m 22 , age: 5±11 years, overweight: n 52Y normal weight: n 8). Methods: 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 (VO 2 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: #1 h of TV per day (group I) and .1 h of TV per day (group II). Results: 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 , 0X05 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 VO 2 submax but reduced adjusted VO 2 submax P , 0X05). They also had parents with a lower educational level P , 0X05X 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 21) and very high (.3 h day 21 ) TV viewing. Conclusions: 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 VO 2 , muscle strength or poor dietary intake. Increased TV consumption is associated with a low SES. Keywords Physical inactivity Activity Energy expenditure Childhood obesity Childhood nutritionIn Western societies overweight and obesity are epidemic and their incidence is increasing. Present data show that children are also getting fatter 1±3 . Environmental factors frequently discourage physical activity and promote overeating, thus supporting childhood obesity 1±4 . A low level of physical activity is considered as an increased risk factor of obesity 1,5±9 . Reduced physical activity results in a reduction in total energy expenditure (TEE), favouring a positive energy balance. However, the relationship between childhood obesity and energy expenditure or physical activity is far from clear. Obese subjects did not consistently show reduced activity 10,11 . Doubly labelled water (DLW) techniques, heart rate (HR) monitoring and accelerometers have been used to assess energy expenditure and physical activity directly in children and adults 9,12±15 . In addi...

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The purpose of the present study was to assess different aspects of physical activity and fitness in order to develop a basis for sport programmes for overweight and obese children. Eighty-eight prepubertal children (49 boys, 39 girls, 4.8-11.4 years old, 61% obese, 14% overweight and 25% normal weight) were examined. Body composition was assessed by combined use of anthropometrics and bioelectrical impedance analysis. Resting energy expenditure (REE) and total energy expenditure (TEE) were measured by indirect calorimetry (IC) and individually calibrated 24-h heart rate (HR) monitoring, respectively. Activity-related energy expenditure (AEE) and physical activity level (PAL) were calculated from TEE and REE. Fitness [assessed by O2-pulse, respiratory exchange ratio (RER) at submaximal work intensities] was determined by ergometry. The maximal isometric muscle strength of the legs (m. quadriceps, Fa max, m. ischiocruralis, Fb max) was measured by computer tensiometry. Children were grouped according to their nutritional state, AEE, O2-pulse and muscle strength. When compared with normal weight children, obese and overweight children had increased fat mass (FM), fat-free mass (FFM), waist-to-hip ratio and REE, but no group differences were observed for TEE, AEE, and PAL. Obese and overweight children spent more hours per day watching TV. After correction for body weight and FFM, no group differences in REE were observed, but normal weight children had a higher O2-pulse than overweight and obese children. By contrast, RER was increased in the latter group. The fittest group had the lowest body weight, BMI, FM and FFM. Children with a low O2-pulse spent more hours per day watching TV. Grouping children according to their degree of muscle strength, younger children (4-7.5 years) did not show group differences in nutritional state, energy expenditure, physical activity and fitness. However, in the group of 7.6- to 11-year-old children, those with the greatest muscle strength and FFM had reduced BMI, skin folds, FM and FFM. FM correlated inversely with O2-pulse, but was not associated with TEE, AEE, PAL or muscle strength. By contrast TV consumption was positively associated with FM. To summarize, overweight and obese children were less fit and watched more TV than their normal weight counterparts. FM did not correspond to TEE, AEE or PAL. Muscle strength was not associated with FM in young children, but was inversely associated with FM in older children. Our cross-sectional data are consistent with the idea that increased fitness and reduced physical inactivity may prevent children from being overweight.

In order to study the kinetics of inactivation and recovery of the slow inward current in the mammalian ventricular myocardium voltage clamp experiments using the double sucrose gap technique were performed on isolated trabeculae and papillary muscles of cats. The separation of the slow inward current from the fast Na current was achieved by use of the conditioning clamp procedure. 1. The decay of the Ca current reflects the inactivation which develops due to depolarization. The rate of inactivation depends upon the membrane potential. Excess Ca (8.8 mM) accelerates the inactivation speed indicating that Ca ions not only act as charge carrier of the slow inward current but might influence in addition the kinetics of the slow membrane channel. In the presence of a lowered temperature a deceleration of inactivation (Q10 2.3) occurs. 2 If the membrane is repolarized a recovery process takes place restoring the availability of the slow membrane channel. As the inactivation the recovery rate depends upon the membrane potential. Excess Ca causes an acceleration whereas a decrease in temperature diminishes the recovery speed (Q10 2.3). Consequently, the Ca supply to the myocardial cell can be modified not only by changes of the transmembrane Ca concentration gradient or by an alteration of the Ca conductance of the slow channel but also by changes in the degree of recovery after a preceding Ca current. 3. Compared with the inactivation the recovery proceeds very slowly. Assuming that this slow recovery represents an inherent kinetic feature of the slow channel the kinetics of inactivation and removal of inactivation are not describable by a single inactivation variable (called as f by Reuter, 1973) which is of the Hodgkin-Huxley type. If a second inactivation variable (called as l) would be introduced additionally a formulation of the inactivation-recovery process of the slow membrane channel on the basis of the Hodgkin-Huxley model becomes feasible.