Tobias Jon H, Steer Colin D, Mattocks Calum G, Riddoch Chris, Ness Andy R
University of Bristol, UK.
J Bone Miner Res. 2007 Jan;22(1):101-9. doi: 10.1359/jbmr.060913.
We examined the influence of habitual levels of physical activity on bone mass in childhood by studying the relationship between accelerometer recordings and DXA parameters in 4457 11-year-old children. Physical activity was positively related to both BMD and bone size in fully adjusted models. However, further exploration revealed that this effect on bone size was modified by fat mass.
Exercise interventions have been reported to increase bone mass in children, but it is unclear whether levels of habitual physical activity also influence skeletal development.
We used multivariable linear regression to analyze associations between amount of moderate and vigorous physical activity (MVPA), derived from accelerometer recordings for a minimum of 3 days, and parameters obtained from total body DXA scans in 4457 11-year-old boys and girls from the Avon Longitudinal Study of Parents and Children. The influence of different activity intensities was also studied by stratification based on lower and higher accelerometer cut-points for moderate (3600 counts/minute) and vigorous (6200 counts/minute) activity, respectively.
MVPA was positively associated with lower limb BMD and BMC adjusted for bone area (aBMC; p < 0.001, adjusted for age, sex, socio-economic factors, and height, with or without additional adjustment for lean and fat mass). MVPA was inversely related to lower limb bone area after adjusting for height and lean mass (p = 0.01), whereas a positive association was observed when fat mass was also adjusted for (p < 0.001). Lower limb BMC was positively related to MVPA after adjusting for height and lean and fat mass (p < 0.001), whereas little relationship was observed after adjusting for height and lean mass alone (p = 0.1). On multivariable regression analysis using the fully adjusted model, moderate activity exerted a stronger influence on lower limb BMC compared with light activity (light activity: 2.9 [1.2-4.7, p = 0.001]; moderate activity: 13.1 [10.6-15.5, p < 0.001]; regression coefficients with 95% confidence intervals and p values).
Habitual levels of physical activity in 11-year-old children are related to bone size and BMD, with moderate activity exerting the strongest influence. The effect on bone size (as reflected by DXA-based measures of bone area) was modified by adjustment for fat mass, such that decreased fat mass, which is associated with higher levels of physical activity, acts to reduce bone size and thereby counteract the tendency for physical activity to increase bone mass.
我们通过研究4457名11岁儿童的加速度计记录与双能X线吸收法（DXA）参数之间的关系，探讨了儿童期习惯性身体活动水平对骨量的影响。在完全调整模型中，身体活动与骨密度和骨骼大小均呈正相关。然而，进一步探究发现，这种对骨骼大小的影响会受到脂肪量的调节。
据报道，运动干预可增加儿童的骨量，但尚不清楚习惯性身体活动水平是否也会影响骨骼发育。
我们使用多变量线性回归分析了来自雅芳亲子纵向研究的4457名11岁男孩和女孩中，至少3天的加速度计记录得出的中等强度和剧烈身体活动（MVPA）量，与全身DXA扫描获得的参数之间的关联。还分别根据中等强度（3600次/分钟）和剧烈强度（6200次/分钟）活动的加速度计切点高低进行分层，研究了不同活动强度的影响。
在调整了骨面积（aBMC；p<0.001，根据年龄、性别、社会经济因素和身高进行调整，无论是否进一步调整瘦体重和脂肪量）后，MVPA与下肢骨密度和骨矿含量呈正相关。在调整身高和瘦体重后，MVPA与下肢骨骼面积呈负相关（p=0.01），而在同时调整脂肪量后则观察到正相关（p<0.001）。在调整身高、瘦体重和脂肪量后，下肢骨矿含量与MVPA呈正相关（p<0.001），而仅调整身高和瘦体重时关系不大（p=0.1）。在使用完全调整模型的多变量回归分析中，与轻度活动相比，中等强度活动对下肢骨矿含量的影响更强（轻度活动：2.9[1.2 - 4.7，p = 0.001]；中等强度活动：13.1[10.6 - 15.5，p<0.001]；回归系数及95%置信区间和p值）。
11岁儿童的习惯性身体活动水平与骨骼大小和骨密度相关，中等强度活动的影响最强。对骨骼大小（以基于DXA的骨面积测量反映）的影响会因调整脂肪量而改变，即与较高身体活动水平相关的脂肪量减少会降低骨骼大小，从而抵消身体活动增加骨量的趋势。
