Maintaining proper bone health is part of every child’s upbringing—it’s why kids are encouraged to drink their milk. A study out of Sweden suggests that increasing the number of physical education classes could benefit bone mass, structure, and strength, but only among girls.
The study aimed to check whether extra physical education classes would impact various bone parameters in growing (pre-pubescent) children. To test this, 170 kids (72 girls, 98 boys) from one Swedish school were given 200 minutes of physical education per week. Three other schools (44 girls and 47 boys each) continued with the standard 60 minutes. The schools involved were from the same general area and had similar socioeconomic and ethnic makeups, which helps minimize possible confounding variables.
After seven years, the children’s bones were examined. It was found that the girls had 2.5% greater cortical thickness and a 6.9% greater polar stress-strain index at the 66% tibia. Since that last sentence probably didn’t make sense, some quick terminology needs to be explained:
- “Cortical thickness” refers to how thick the cortical (outermost) tissue of the bone is.
- The polar stress-strain index is a way of providing a surrogate measure for bone strength. Running calculations on a bone scan is not the most direct way of determining bone strength, but is the best option since most bones are currently in use.
- The “66% tibia” refers to a location on the tibia (shin) that is closest to the top of the bone.
In other words, the tibias of the girls in the study had thicker outer layers and were stronger along the uppermost section of the bone.
The findings were independent of the children’s age, weight, or bone length, which means the results were likely from the exercise activity itself rather than individual differences. The fact that none of the boys showed significant changes in their bone parameters is a bit odd, but the researchers did try and explain it. They theorized that the boys were more active in their spare time and were already engaged in a variety of exercise and weight-bearing activities. If the boys were already getting at least three hours of physical activity per week, then the extra physical education classes would not have much extra impact. If true, the findings may also be taken to suggest that bone health could be better promoted by encouraging pre-pubescent girls to engage in more physical activity outside of school hours.
Fritz, J., et. al., “Influence of a School-based Physical Activity Intervention on Cortical Bone Mass Distribution: A 7-year International Study,” Calcified Tissue International, 2016; 10.1007/s00223-016-0174-y.
“Extra physical education classes may benefit bone health in girls, study shows” International Osteoporosis Foundation web site, September 7, 2016; https://www.iofbonehealth.org/news/extra-physical-education-classes-may-benefit-bone-health-girls-study-shows, last accessed September 8, 2016.