Table 1.
Association Between Physical Activity Change and Change in Weight-Bearing Bone Parameters in Young Men
| Physical activity | |||||||
|---|---|---|---|---|---|---|---|
| Baseline | Change | ||||||
| Five-year changea (mean ± SD) | B-absolute | B-relative (%) | B-absolute | B-relative (%) | R2 (%) | Osteogenic index change, R2 (%) | |
| Measurement site for BMC, aBMD, and bone area using DXA | |||||||
| Total body BMC (g)b | 135 ± 160 | 5.5*** | 0.16*** | 5.4** | 0.19*** | 1.2 | 2.1 |
| Lumbar spine aBMD (g/cm2)b | 0.046 ± 0.061 | 0.003*** | 0.24*** | 0.005*** | 0.37*** | 6.0 | 4.8 |
| Total hip aBMD (g/cm2)b | –0.023 ± 0.061 | 0.003*** | 0.25*** | 0.004*** | 0.38*** | 5.6 | 5.9 |
| Lumbar spine area (cm2)b | 1.04 ± 1.50 | 0.03* | 0.05 | 0.08*** | 0.13*** | 3.3 | 3.0 |
| Femoral neck area (cm2)b | 0.089 ± 0.129 | 0.005*** | 0.08*** | 0.005*** | 0.08*** | 1.4 | – |
| Measurement site for vBMD, bone size, and bone strength at the tibia using pQCT | |||||||
| Cortical | |||||||
| Cross sectional area (mm2)c | 11.30 ± 8.71 | 0.59*** | 0.18*** | 0.36*** | 0.13*** | 1.8 | 2.6 |
| Periosteal circumference (mm)c | –0.39 ± 1.01 | 0.027* | 0.04** | 0.027** | 0.04** | 0.8 | 1.7 |
| Endosteal circumference (mm)c | –2.18 ± 1.73 | –0.038* | –0.07 | –0.005 | –0.01 | – | – |
| vBMD (mg/cm3)c | 7.49 ± 13.45 | –0.37** | –0.03** | –0.18 | –0.02 | – | 0.6 |
| Polar SSI (mm3)c | 111 ± 63 | 3.24*** | 0.13** | 1.59* | 0.09* | 0.7 | 0.7 |
| Trabecular | |||||||
| vBMD (mg/cm3)d | –4.70 ± 14.24 | 0.55*** | 0.21*** | 0.59*** | 0.22*** | 1.9 | 2.6 |
| Total | |||||||
| Cross sectional area (mm2)c | –4.16 ± 17.37 | 0.56** | 0.26** | 0.49** | 0.19* | 0.9 | 2.2 |
Linear regression model with change in bone parameters as dependent variables, adjusted for follow-up time. Baseline physical activity (h/week) or osteogenic index and physical activity change (h/week) or osteogenic index change between the baseline and follow-up visit were used as independent and continuous variables. Main effects of independent variables are presented as unstandardized coefficients (B). B-absolute denotes B for absolute change in bone variables while B-relative denotes B for percentage change in bone variables per hour change.
BMC = bone mineral content; aBMD = areal bone mineral density; DXA = dual-energy X-ray absorptiometry; vBMD = volumetric bone mineral density; pQCT = peripheral quantitative computed tomography; polar SSI = strength strain index with respect to torsion; R2 = percentage of the variation.
Five-year changes have been reported previously.(19)
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