Childhood obesity is a global problem, e.g., due to physical inactivity. External skeletal robustness (Frame-Index) has decreased in German schoolchildren. An association between Frame-Index and physical activity was assumed. Further often body mass index (BMI) is analyzed without reference to bone structure. Therefore, we analyze relationships between Frame-Index, BMI, % body fat, and physical activity.


In a cross-sectional study, 691 German children aged 6–10 years were investigated. BMI, % body fat, Frame-Index, total steps p.w., sports club rate p.w., training time p.d., and TV-time p.d. were determined.


Total steps (P < 0.001), BMI (P < 0.001), and % body fat (P = 0.024) are positively linked to Frame-Index. Total steps (P < 0.001), sports club rate (P = 0.001), and training time (P < 0.001) are negatively associated with % body fat. Total steps (P = 0.017) are negatively linked to BMI. TV-time is positively related to BMI (P < 0.001) and % body fat (P < 0.001). % Body fat is affected by age (P < 0.001), sex (P = 0.028), and total steps (P = 0.002). BMI is influenced by age (P < 0.001), and Frame-Index by sex (P < 0.001) and total steps (P = 0.029). Principal component analysis indicates an association between BMI and TV-time and Frame-Index and total steps.


We demonstrate an association between external skeletal robustness and physical activity, which is not captured by in BMI measurements. Children should be physically active in order to maintain skeletal robustness. Am. J. Hum. Biol. 25:404–410, 2013. © 2013 Wiley Periodicals, Inc.