A new study from UBC and the Vancouver Coastal Health Research Institute finds that inactive teens produce weaker bones, a problem that affects bone strength for one’s whole life. The results provide more evidence of the importance of exercise and physical activity during developmental years, a challenge these days where children and adolescents have developed more sedentary behaviours prominently featuring computer and electronic devices.
Researchers for the study took annual measurements conducted between May 2008 and June 2012 of the tibia and radius bones of 173 girls and 136 boys, aged between eight and 12 years at the commencement of the study. Physical activity for the participants was tracked with accelerometers worn by the youth for seven consecutive days at a time, while bone microarchitechture, bone geometry, mineral density and bone strength were assessed through high resolution 3D cross-sectional x-ray scans of the tibia and radius.
The results showed that only 24 per cent of the youth involved in the study (43 per cent of the boys, nine per cent of the girls) met the recommendation of 60 minutes of moderate to vigorous physical exercise per day. The researchers found that those youth who did get their 60 minutes a day of exercise had approximately four per cent greater bone volume in comparison to youth who had less than 30 minutes per day of exercise. Overall, physical activity was found to be an independent predictor of bone strength for youth.
“Our results suggest that adolescents who participate in more intense physical activity (MVPA) have greater trabecular bone tissue volume at both skeletal sites and greater bone area at the tibia, which contribute to superior bone strength,” say the study’s authors.
During a crucial four-year window in adolescence (between 10 and 14 for girls and 12 and 16 for boys), as much as 36 per cent of the human skeleton is formed, and bones respond to physical activity, especially the kind with jolting movements like jumping jacks, skipping rope or dancing.
“The skeleton is a different than the cardiovascular system that it really likes sharp short bursts of exercise,” says Heather McKay, study co-author and professor in orthopedics and family practice at UBC and the Centre for Hip Health and Mobility at the Vancouver Coastal Health Research Institute. “A third of your skeleton is laid down in just four years in your adolescence,” says McKay. “When you get past that, [your] skeleton is fully formed. Then it’s about hanging on to the bone structure that you have for as long as you can.”
Nationwide, only nine per cent of children between the ages of five and 17 get the recommended 60 minutes of exercise per day, according to Health Canada. Too much screen time and sedentary activities are the culprits, along with children and youth actually being too tired to get their exercise. Children’s nightly sleep duration has reportedly decreased by between 30 and 60 minutes over recent decades and 31 per cent of school-aged children in Canada are sleep deprived.
The new study was published in the Journal of Bone and Mineral Research.