Relationships between physical activity, physical fitness, muscle strengthand nutritional state in 5-to 11-year-old children

The purpose of the present study was to assess different aspects of physica l 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 wei ght) were examined. Body composition was assessed by combined use of anthro pometrics and bioelectrical impedance analysis. Resting energy expenditure (REE) and total energy expenditure (TEE) were measured by indirect calorime try (IC) and individually calibrated 24-h heart rate (HR) monitoring, respe ctively. Activity-related energy expenditure (AEE) and physical activity le vel (PAL) were calculated from TEE and REE. Fitness [assessed by O-2-pulse, respiratory exchange ratio (RER) at submaximal work intensities] was deter mined by ergometry. The maximal isometric muscle strength of the legs (m, q uadriceps, Fa max, m. ischiocruralis, Fb max) was measured by computer tens iometry. Children were grouped according to their nutritional state, AEE, O -2-pulse and muscle strength. When compared with normal weight children, ob ese 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 T EE, AEE, and PAL. Obese and overweight children spent more hours per day wa tching TV. After correction for body weight and FFM, no group differences i n REE were observed, but normal weight children had a higher O-2-pulse than overweight and obese children. By contrast, RER was increased in the latte r group. The fittest group had the lowest body weight, BMI, FM and FFM. Chi ldren with a low O-2-pulse spent more hours per day watching TV. Grouping c hildren according to their degree of muscle strength, younger children (4-7 .5 years) did not show group differences in nutritional state, energy expen diture, 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 redu ced BMI, skin folds, FM and FFM. FM correlated inversely with O-2-pulse, bu t 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 wit h FM in older children. Our cross-sectional data are consistent with the id ea that increased fitness and reduced physical inactivity may prevent child ren from being overweight.