Background
Methods
Study
Study sample
Bone mineral content measurement
Self reported measures of physical activity and sedentary behaviours
Objective physical activity and sedentary behaviour monitoring and data processing
Statistical data analysis
Results
Variables |
Male
| Female |
---|---|---|
Age (year)
| 14.0 [8 – 22] | 13.6 [8 – 22] |
Spinal BMCa
(g)
| 46.4 [16.2 – 100.1] | 43.5 [13.2 – 85.6] |
Femoral BMCa
(g)
| 31.7 [9.3 – 67.2] | 24.9 [55.7 – 7.54] |
BMIb
(kg/m
2
)
| 22.0 [12.8 – 54.4] | 22.5 [12.4 – 50.4] |
Sedentary time (%)
| 52.6 [21.2 – 90.6]* | 55.1 [14.8 – 79.1]* |
MVPAc
(%)
| 23.2 [0.0 – 51.0]* | 20.4 [0.0 – 74.0]* |
TV watching (hours/day)
| 3.3 [1 – 6] | 3.2 [1 – 6] |
Computer use (hours/day)
| 2.3 [0 – 6]* | 2.0 [0 – 6]* |
Frequency of vigorous playing/exercising (number per week)
| 6.1 [0 – 21]* | 5.4 [0 – 21]* |
Frequency of strengthening activities (number per month)
| 11.5 [0 – 180]* | 7.0 [0 – 60]* |
Model | Model R2
adj
| B (95% CI) | βa
|
---|---|---|---|
R2change | |||
Model 1
| 0.673 | ||
Model adjusted for | |||
Age (β = 0.704)***, BMI (β = 0.231) ***, Ethnicity (β = 0.101)*** and Vitamin D (β = 0.076)***
| |||
Objective sedentary time | 0.000 | −1.09 (−4.66 to 6.76) | 0.009 |
Time spent watching TV |
0.002
*
|
−0.44 (−0.84 to −0.05)
*
|
−0.053
|
Time spent on computer | 0.001 | −0.41 (−0.96 to 0.14) | −0.035 |
Total screen time |
0.002
*
|
−0.21 (−0.41 to 0.00)
*
|
−0.046
|
Total non-screen SB | 0.002 | 0.17 (−0.01 to 0.35) | 0.044 |
α | 0.000 | −1.36 (−4.24 to 1.51) | −0.023 |
Model 2
| 0.687 | ||
Model 1 adjusted for objectively measured MVPA (β = 0.144) ***
| |||
Objective sedentary time |
0.009
***
|
15.93 (8.64 to 23.11)
***
|
0.143
|
Time spent watching TV |
0.002
*
|
- 0.45 (−0.83 to −0.06)
*
|
−0.053
|
Time spent on computer | 0.000 | −0.35 (−0.89 to 0.19) | −0.030 |
Total screen time | 0.001 | −0.82 (−1.80 to 0.16) | −0.039 |
Total non-screen SB |
0.006
**
|
0.327 (0.141 to 0.513)
**
|
0.095
|
α |
0.006
***
|
−5.67 (−8.86 to −2.49)
***
|
−0.096
|
Model 3
| 0.415 | ||
Model 1 adjusted for weekly frequency of strengthening exercise (β = 0.102) **
| |||
Objective sedentary time | 0.000 | −1.26 (−8.37 to 5.85) | −0.013 |
Time spent watching TV | 0.002 | − 0.48 (−0.97 to 0.02) | −0.071 |
Time spent on computer | 0.000 | −0.41 (−1.21 to 0.34) | −0.038 |
Total screen time | 0.003 | −0.90 (−2.19 to 0.38) | −0.052 |
Total non-screen SB | 0.001 | 0.13 (−0.11 to 0.36) | 0.038 |
α | 0.000 | −0.27 (−0.40 to 0.34) | −0.005 |
Model 4
e
| 0.510 | ||
Model 1 adjusted for weekly frequency of vigorous playing or exercise (β = 0.126)*
| |||
Objective sedentary time | 0.002 | −3.13 (−9.03 to 2.78) | −0.061 |
Time spent watching TV | 0.001 | 0.114 (−0.28 to 0.47) | 0.036 |
Time spent on computer | 0.004 | −0.24 (−0.60 to 0.12) | −0.076 |
Total screen time | 0.000 | 0.12 (−0.71 to 0.96) | 0.017 |
Total non-screen time SB | 0.000 | −0.03(−0.18 to 0.13) | −0.021 |
α | 0.000 | −1.88 (−7.15 to 3.40) | −0.08 |
Model | Model R2
adj
| B (95% CI) | βa
|
---|---|---|---|
R2change | |||
Model 1
| 0.655 | ||
Model adjusted for age (β = 0.377)***, age of first menstrual cycle (β = −0.236)***, BMI (β = 0.377)*** and Ethnicity (β = 0.086)***
| |||
Objective sedentary time | 0.000 | 0.21 (−3.67 to 4.19) | 0.003 |
Time spent watching TV |
0.003
*
|
−0.28 (−0.50 to −0.06)
*
|
−0.057
|
Time spent on computer | 0.000 | −0.18 (−0.54 to 0.19) | −0.022 |
Total screen time |
0.004
**
|
−0.80 (−1.35 to −0.25)
**
|
−0.066
|
Total non-screen SB |
0.004
**
|
0.15 (0.04 to 0.26)
**
|
0.063
|
α | 0.001 | −1.41 (−3.28 to 0.47) | −0.038 |
Model 2
| 0.662 | ||
Model 1 adjusted for objectively measured MVPA (β = 0.130)***
| |||
Objective sedentary time |
0.005
***
|
8.07 (3.18 to 12.97)
***
|
0.113
|
Time spent watching TV |
0.003
*
|
- 0.26 (−0.48 to −0.05)
*
|
−0.055
|
Time spent on computer | 0.000 | −0.16 (−0.52 to 0.20) | −0.020 |
Total screen time |
0.004
**
|
−0.77 (−1.31 to −0.22)
**
|
−0.063
|
Total non-screen SB |
0.006
**
|
0.327 (0.141 to 0.513)
**
|
0.095
|
α |
0.007
***
|
−4.05 (−6.18 to −1.92)
***
|
−0.109
|
Model 3
| 0.415 | ||
Model 1 adjusted for weekly frequency of strengthening exercise (β = 0.173)***
| |||
Objective sedentary time | 0.002 | −3.21 (−8.25 to 1.81) | −0.049 |
Time spent watching TV |
0.009
*
|
− 0.33 (−0.59 to −0.07)
*
| −0.095 |
Time spent on computer | 0.000 | −0.10 (−0.56 to 0.35) | −0.017 |
Total screen time |
0.009
*
|
−0.86 (−1.54 to −0.17)
*
| −0.095 |
Total non-screen SB | 0.004 | 0.11 (−0.02 to 0.25) | 0.064 |
α | 0.000 | 0.842 (−1.72 to 3.41) | 0.025 |
Model 4
| 0.577 | ||
Model 1 adjusted for weekly frequency of vigorous playing or exercise (β = 0.140)**
| |||
Objective sedentary time | 0.003 | −3.15 (−7.85 to 1.55) | −0.061 |
Time spent watching TV | 0.004 | 0.23 (−0.11 to 0.55) | 0.065 |
Time spent on computer | 0.000 | −0.03 (−0.47 to 0.41) | −0.006 |
Total screen time | 0.001 | 0.26 (−0.45 to 0.97) | 0.034 |
Total non-screen time SB | 0.000 | −0.08 (−0.23 to 0.07) | −0.048 |
α | 0.000 | −0.513(−1.59 to 2.61) | 0.022 |
Model | Model R2
adj
| B (95% CI) | βa
|
---|---|---|---|
R2change | |||
Model 1
| 0.701 | ||
Model adjusted for Age (β = 0.771)***, BMI (β = 0.153)***, Ethnicity (β = 0.094)*** and Vitamin D (β = 0.093)***
| |||
Objective sedentary time | 0.001 | 5.33 (−3.11 to 13.78) | 0.031 |
Time spent watching TV | 0.001 | −0.47 (−1.06 to 0.12) | −0.036 |
Time spent on computer | 0.001 | −0.51 (−1.32 to 0.31) | −0.028 |
Total screen time | 0.001 | −1.17 (−2.60 to 0.25) | −0.037 |
Total non-screen SB | 0.000 | 0.07 (−0.07 to 0.20) | 0.021 |
α | 0.002 | −3.16 (−7.47 to 1.15) | −0.034 |
Model 2
| 0.708 | ||
Model 1 adjusted for objectively measured MVPA (β = 0.097)**
| |||
Objective sedentary time |
0.009
***
|
24.10 (13.22 to 34.99)
***
|
0.139
|
Time spent watching TV | 0.001 | − 0.48 (−1.06 to 0.10) *
| −0.036 |
Time spent on computer | 0.001 | −0.45(−1.26 to 0.37) | −0.024 |
Total screen time | 0.001 | −1.08(−2.50 to 0.34) | −0.034 |
Total non-screen SB | 0.001 | 0.04(−0.04 to 0.232)**
| 0.031 |
α |
0.005
**
|
−8.23 (−13.06 to −3.39)
***
|
−0.090
|
Model 3
| 0.482 | ||
Model 1 adjusted for weekly frequency of strengthening exercise (β = 0.099)**
| |||
Objective sedentary time | 0.001 | 5.51 (−5.25 to 16.27) | 0.036 |
Time spent watching TV | 0.004 | - 0.69 (−1.44 to 0.07) | −0.063 |
Time spent on computer | 0.002 | −0.84 (−2.06 to 0.39) | −0.047 |
Total screen time | 0.004 | −1.86 (−3.83 to 0.11) | −0.066 |
Total non-screen SB |
0.004
*
|
0.36 (0.00 to 0.72)
*
|
0.067
|
α | 0.002 | −3.32(−8.99 to 2.36) | −0.040 |
Model 4
| 0.378 | ||
Model 1 adjusted for weekly frequency of vigorous playing or exercise (β = 0.048) | |||
Objective sedentary time | 0.000 | −0.799 (−8.79 to 7.19) | −0.013 |
Time spent watching TV | 0.005 | 0.276 (−0.21 to 0.76) | 0.073 |
Time spent on computer | 0.000 | −0.06 (−0.55 to 0.43) | −0.016 |
Total screen time | 0.001 | 0.27 (−0.46 to 0.99) | 0.028 |
Total non-screen time SB | 0.000 | −0.01 (−0.05 to 0.07) | 0.018 |
α | 0.001 | −0.78 (−4.39 to 2.84) | −0.028 |
Model | Model R2
adj
| B (95% CI) | βa
|
---|---|---|---|
R2change | |||
Model 1
| 0.643 | ||
Model adjusted for age (β = 0.692)***, BMI (β = 0.197)*** and Ethnicity (β = 0.081)**
| |||
Objective sedentary time |
0.007
***
|
14.13 (6.31 to 21.96)
***
|
0.096
***
|
Time spent watching TV |
0.003
*
|
−0.49 (−0.95 to 0.02)
*
|
−0.049
*
|
Time spent on computer | 0.001 | −0.53 (−1.29 to 0.29) | −0.032 |
Total screen time |
0.005
**
|
−0.40(−0.66 to -0.15)
**
|
−0.073
**
|
Total non-screen SB |
0.010
***
|
0.49(0.27 to 0.71)
***
|
0.102
***
|
α |
0.006
**
|
−6.74 (−10.62 to -2.86)
**
|
−0.087
**
|
Model 2
| 0.702 | ||
Model 1 adjusted for objectively measured MVPA (β = 0.057) | |||
Objective sedentary time |
0.008
***
|
23.63 (12.91 to 34.35)
***
|
0.137
***
|
Time spent watching TV |
0.001
*
|
- 0.58 (−1.13 to -0.03)
*
|
−0.044
*
|
Time spent on computer | 0.001 | −0.61(−1.40 to 0.176) | −0.033 |
Total screen time | 0.001 | −0.08(−0.22 to 0.06) | −0.023 |
Total non-screen SB |
0.013
***
|
0.58(0.35 to 0.805)
***
|
0.121
***
|
α |
0.013
***
|
−11.24(−15.69 to -6.79)
***
|
−0.146
***
|
Model 3
| 0.276 | ||
Model 1 adjusted for weekly frequency of strengthening exercise (β = 0.168)***
| |||
Objective sedentary time | 0.000 | 0.86 (−9.59 to 11.31) | 0.007 |
Time spent watching TV | 0.005 | −0.46(−1.00 to 0.09) | −0.069 |
Time spent on computer | 0.001 | −0.30 (−1.26 to 0.65) | −0.026 |
Total screen time |
0.007
*
|
−0.34 (−0.65 to -0.03)
*
|
−0.089
*
|
Total non-screen SB | 0.006 | 0.27 (−0.01 to 0.54) | 0.080 |
α | 0.000 | 0.03(−5.39 to 5.45) | 0.000 |
Model 4
| 0.470 | ||
Model 1 adjusted for weekly frequency of vigorous playing or exercise (β = 0.101)*
| |||
Objective sedentary time | 0.000 | 0.804 (−8.68 to 10.26) | 0.009 |
Time spent watching TV | 0.001 | 0.181 (−0.48 to 0.838) | 0.030 |
Time spent on computer | 0.001 | −0.20 (−1.08 to 0.67) | −0.023 |
Total screen time | 0.001 | −0.08 (−0.39 to 0.24) | −0.066 |
Total non-screen time SB | 0.001 | 0.08 (−0.21 to 0.37) | 0.028 |
α | 0.000 | −0.72 (−4.95 to 3.51) | −0.028 |