Effects of a daily school based physical activity intervention program on muscle development in prepubertal girls

This 12-month prospective controlled intervention evaluated the effect of a general school based physical activity program on muscle strength, physical performance and body composition in prepubertal girls. Fifty-three girls aged 7&ndash;9 years involved in a school based exercise program [40 min/day of general physical activity per school day (200 min/week)] were compared with 50 age-matched girls who participated in the general Swedish physical education curriculum (mean 60 min/week). Body composition (DXA), isokinetic peak torque (PT) of the knee extensors and flexors at 60 and 180&deg;/s, and vertical jump height (VJH) were assessed at baseline and 12 months. The annual gain in weight was similar between the groups, but there was a greater increase in total body and regional lean mass (P &lt; 0.05) and fat mass (P &lt; 0.01) in the exercise group. Mean gains in knee extensor PT at 60 and 180&deg;/s were 7.0&ndash;7.6% greater in the exercise group (P ranging &lt;0.05&ndash;&lt;0.001). No significant differences were detected in VJH. In conclusion, increasing school based physical education to at least 3 h/week provides a feasible strategy to enhance the development of muscle strength and lean mass in prepubertal girls.<br /

Weight-bearing bones are more sensitive to physical exercise in boys than in girls during pre- and early puberty: a cross-sectional study.

We carried out a cross-section study of the sex-specific relationship between bone mineral content and physical activity at sites with different loading in pre- and early pubertal girls and boys. There was significant sensitivity of bone mineral content of the hip to physical exercise in boys, but not in girls. BACKGROUND: Since little is known whether there are sex differences in sensitivity of bone to loading, we investigated sex differences in the cross-sectional association between measures of physical activity (PA) and bone mass and size in pre- and early pubertal children of both sexes. METHODS: We measured bone mineral content/density (BMC/BMD) and fat-free mass (FFM) in 269 6- to 13-year-old children from randomly selected schools by dual-energy X-ray absorptiometry. Physical activity (PA) was measured by accelerometers and lower extremity strength by a jump-and-reach test. RESULTS: Boys (n = 128) had higher hip and total body BMC and BMD, higher FFM, higher muscle strength and were more physically active than girls (n = 141). Total hip BMC was positively associated with time spent in total and vigorous PA in boys (r = 0.20-0.33, p &lt; 0.01), but not in girls (r = 0.02-0.04, p = ns), even after adjusting for FFM and strength. While boys and girls in the lowest tertile of vigorous PA (22 min/day) did not differ in hip BMC (15.62 vs 15.52 g), boys in the highest tertile (72 min/day) had significantly higher values than the corresponding girls (16.84 vs 15.71 g, p &lt; 0.05). CONCLUSIONS: Sex differences in BMC during pre- and early puberty may be related to a different sensitivity of bone to physical loading, irrespective of muscle mass

Relationship among explosive power, body fat, fat free mass and pubertal development in youth soccer players: a preliminary study

Purpose: Changes in body size and functional capacities are highly individual during puberty, and the performance of a soccer player is often closely related to their maturity status. The aim of the study was to evaluate the relationships among explosive power, body fat, fat free mass and pubertal development in young soccer players. Methods: Explosive power (countermovement jump-CMJ), body mass index (BMI), percentage of body fat (¿), fat free mass (FFM) and a Self-Administered Rating Scale for pubertal development (PDS) values of 11 "Giovanissimi" (age 13 year), 13 "Allievi" (age 15 year) and 10 "Juniores" (age >17 year) male soccer players were compared. The statistical analysis was performed using an analysis of variance among categories with Fisher's post hoc as appropriate. Furthermore, Pearson correlations among variables were calculated considering all subjects and also within categories. Results: Statistical differences emerged among categories in CMJ (F (2,30) = 28.3, p < 0.01), body fat weight (F (2,31) = 29.2, p < 0.01) and PDS (F (2,29) = 18.5, p < 0.01), while ¿ values showed statistical differences only for "Giovanissimi" and "Juniores" (F (2,31) = 3.4, p = 0.01). CMJ showed significant correlations with FFM (r = 0.68) and PDS (r = 0.63), PDS with FFM (r = 0.66) and BMI with ¿ (r = 0.71) and FFM (r = 0.71). A high correlation was found within categories. Conclusion: Since we found differences between categories and no correlation between chronological age and pubertal status, this study highlights the importance of assessing of puberty in youth soccer team