Boys: Physical Activity and Strength Training Interview with:
Chris Fritz BSs
PEZZ Center for Pediatric Endocrinology Zurich, Zurich, Switzerland What are the main findings of the study?

Answer: Targeted strength training significantly increases daily spontaneous physical activity (PA) behaviour in boys. The less active children showed the greatest increase.

102 healthy school children were randomly placed in two groups. The control group continued three PE classes per week, whereas the intervention group had two out of three PE classes replaced by an individualised strength training program. At baseline there was no difference in anthropometry, body composition and PAEE between the groups. At the end of the training intervention, we found a significant increase of upper and lower body strength in the intervention group in boys and in girls. Boys significantly increased their PA by 10%. Without taking into account the energy expenditure during the strength training, the 10% PAEE increase corresponds to a weekly bike ride of 28 miles for a child of 40 kg body weight. Or in other words, an individualised school based strength training program increases energy expenditure outside the intervention by an equivalent of about 7kg of body fat corresponding to 10kg of chocolate per year. Were any of the findings unexpected?

Answer: Recently we have shown in children with Prader-Willi-Syndrome (PWS), as well as in healthy junior ice hockey players, that individually targeted strength training induces increased spontaneous PA outside of training. The main objective of this randomised controlled intervention study was to assess whether participation in a structured individualised strength training programme 2 hours per week would increase spontaneous daily PA outside of training in normal school children. We could show that a targeted strength training programme during regular school PE lessons increases the daily amount of spontaneous PA behaviour in boys before puberty and that the strength training programme was most efficient for the children with the lowest PA at the beginning. However, the girls in this study showed the same increase in upper and lower body strength, which suggests that they were similarly motivated, but no increase in daily spontaneous physical activity. We believe that it is not the type of intervention, but the age / pubertal stage which explains the different findings between boys and girls. That the onset of puberty may be responsible for changing patterns of PA from a child regulation to an adult one is supported by our previous observation in junior ice hockey players, where the positive correlation between training intensity and spontaneous PA was lost with the onset of puberty. What should clinicians and patients take away from your report?

Answer: During the last fifty years, lifestyles changed from being physically active to being predominantly sedentary and inactive. Today, the majority of girls and a large proportion of boys fail to meet the minimum target of 60 minutes of at least moderate intensity physical activity per day. Furthermore, PA declines as children get older. The declining physical activity among children could be reversed if more specifically targeted PE classes, for example including strength training, were to become an integral part of physical education. In addition, the positive aspect of the strength training was that every child was able to see its own progress. In addition, children who typically struggled with group activities were able to perform well on the strength training exercises. Seeing their own progress boosted their self-esteem and motivated them to remain engaged. If supervised by a qualified teacher, strength training is safe as already shown by others. No injuries occurred throughout the study period. Schools are well suited to introduce children to strength training as they spend most of their time there and such activities are also much more attractive for children if carried out together with schoolmates. The cost of the equipment required for strength training is low. What recommendations do you have for future research as a result of this study?

Answer: Identifying factors related to changes in physical activity is an important step in developing interventions to stop decreases in physical activity levels during childhood.

Further research is needed to understand the factors that influence PA in pre- and pubertal children and to find out what adequate training stimulus is needed to have a lasting impact on physical activity behaviour. It would be interesting to research, whether an individualised strength training programme 2 hours per week would increase spontaneous daily PA outside of training in girls before onset of puberty. For such a study, girls should be younger than 11.


Strength Training and Physical Activity in Boys: a Randomized Trial
Udo Meinhardt, Fabienne Witassek, Renato Petrò, Chris Fritz, and Urs Eiholzer
Pediatrics peds.2013-1343; published ahead of print November 4, 2013, doi:10.1542/peds.2013-1343