Growing bone can adapt to improve bone strength in response to increased mechanical loads. It can do it through geometrically modeling in a number of ways.
BC Health Research Foundation funded this research. The study appears online in the Journal of Bone and Mineral Research.
What does the research say?
First, bone can increase in specific dimensions through the apposition of new bone to the developing surface. These geometric changes confer a significant structural advantage. It is because the marginal expansion of bone translates into considerable increases in a cross‐sectional moment of inertia. Section modulus as a measure of bone stiffness is closely related to the bending and torsional strength of bone. These structural parameters reflect the optimal redistribution of bone around the neutral axis and other dimensions.
Second, adaptation could occur due to diminished bone resorption from the endocortical surface. An increase in the amount of bone within the periosteal envelope would also improve bone strength.
Changes in bone shape or increases in bone size would not necessarily translate into increased DXA measures of bone mass. However, geometric adaptations in children confer a considerable strength advantage that may be overlooked.
What did the scientists do?
Scientists recruited schools in Canada with a multi‐ethnic population. It included 34% of Hong Kong Chinese and 57% white. Fourteen schools volunteered for the study. A total of 383 students from grades 4, 5, and 6 (ages 9‐12 years), participated. Scientists stratified schools on the basis of ethnic composition and randomly assigned to control and intervention groups. They used a food frequency questionnaire (FFQ) to estimate dietary calcium intake.
Scientists determined the general physical activity using a modified version of the Physical Activity Questionnaire for Children. It assesses daily activity over the past 7 days and scored from 1 (low activity) to 5 (high activity). The questionnaire also included questions regarding loading activity. Additionally, it also included an indication of the number of nights per week the child participated in organized sports. So, they measured three physical activities. An average physical activity (score from 1‐5). Load time (hours per week of weight‐bearing activity). Sports nights (days per week of organized sports).
What did the results suggest?
Scientists noted the control group. There were no significant differences between the groups for height, weight, fat or lean mass, calcium intake, or average physical activity. Change in height and weight did not differ between the intervention.
Data indicate that maturity‐ and site‐specific changes in bone structural variables result from a school‐based jumping intervention. This study shows that intervention in prepubertal girls does not alter the bone structure. However, it might adopt in response to exercise intervention in early‐pubertal girls.