Relationship between Bone Mass and Habitual Physical Activity and Calcium Intake in 8–11-Year-Old Boys and Girls

Abstract

This study aimed to determine the relationship between bone mineral content, habitual physical activity, and calcium intake in children. Fifty-seven children, aged 8–11 years, wore pedometers for seven days to assess activity. Calcium intake was estimated by a 4-day food diary. Bone mineral content (BMC) and areal density (BMD) were measured at the total proximal femur and femoral neck using dual energy X-ray absorptiometry. Regression analysis was used to assess contributions of physical activity and calcium intake to BMC, residualized for bone area and body mass. Physical activity explained 11.6% of the variance in residualized BMC at the proximal femur and 14.3% at the femoral neck (p < 0.05). Calcium intake added to the variance explained at the proximal femur only (9.8%, p < 0.05). This study provides evidence for an association between BMC and habitual physical activity.

The relationship between children's habitual activity level and psychological well‐being

“…This does not support previous research that has consistently shown that boys and girls of this age group differ in activity level 11, 24. Furthermore, in previous research that has measured activity for 5 to 7 d, boys have been shown to be more active than girls 21, 23. There are three possible explanations for this.…”

“…The researchers have no details on the eight children (two girls, six boys) who did not participate in the study. This convenience sample procedure follows that employed by Rowlands and colleagues 13, 15,21, 23. All data were collected within term time.…”

“…Each night the child's parents recorded the number of counts on the pedometer and re‐set the pedometer to zero. This method follows that used in our laboratory in the past with no problems reported by the parents 13, 21, 23. The money belt containing the pedometer was worn for a total of seven consecutive days in line with the guidelines of Trost et al 16 that have shown this to provide reliable estimates of usual physical activity behaviour in children.…”

“…It has consistently shown that accelerometry is the best single measure of acute and chronic activity levels in children and that pedometry (using the Yamax Digiwalker SW‐200, Yamasa, Tokyo, Japan) is also a valid and reliable method. Indeed, pedometry is increasingly being recognized as providing an objective, practical and reliable indicator of total activity 22 and has been used to show positive relationships between energy expenditure and recommended daily activity levels 15 and habitual activity and bone density in children 23. Given the considerably cheaper cost of the Digiwalker™, Rowlands and colleagues 13 recommend the use of them for larger population studies as a means of assessing habitual activity.…”

Calcium and Exercise Affect the Growing Skeleton

“…Many studies examining the effect of calcium intake and exercise on pediatric bone included both factors in multivariate analyses but did not report any examination of interactions between the two. [111][112][113][114][115][116][117][118] Furthermore, it is difficult to interpret exercise effects on the skeleton in studies that present exercise data in terms of intensity, duration, and frequency of cardiovascular exertion 111,112,[114][115][116][119][120][121] For example, Rowlands et al 119 quantified exercise in terms of cardiovascular intensity, expressed as metabolic equivalents, and correlated this with calcium intake in 9-year-old children. This could result in the inclusion of activities with low strain rates, such as walking, bicycling, and water sports, which are known to have little, no, or possibly adverse effects on bone.…”