The minimum intensity of physical activity that is associated with favourable body composition and cardiorespiratory fitness remains unknown. |
This study found that a higher intensity of physical activity was necessary to confer benefits to cardiorespiratory fitness (>3 metabolic equivalents) than to improve levels of total and truncal adiposity (>2 metabolic equivalents) in children aged 6–8 years, but both associations were characterised by a dose-dependent phenomenon. |
Public health bodies might consider formulating recommendations purely around the concept of continuous dose-response relationships, as higher intensity physical activity may be optimal for body composition and cardiorespiratory fitness in mid-childhood, but any right-shift in the intensity distribution is likely to be beneficial. |
1 Introduction
2 Subjects and Methods
2.1 Sample
2.2 Assessment of Body Size and Composition
2.3 Assessment of Cardiorespiratory Fitness
2.4 Assessment of Physical Activity and Sedentary Time
2.5 Other Assessments
2.6 Statistics
3 Results
3.1 Sample Description
Parameter | Boys (n = 202) | Girls (n = 208) |
p for sex difference | ||
---|---|---|---|---|---|
n
| Value |
n
| Value | ||
Age (y) | 202 | 7.7 ± 0.4a
| 208 | 7.6 ± 0.4 | 0.089 |
Ethnicity (n (%) White) | 202 | 197 (97.5) | 208 | 203 (97.6) | 0.96 |
Household income (n (%)) | 194 | 206 | |||
Low |
–
| 37 (19.1) | – | 45 (21.8) | |
Middle |
–
| 76 (39.2) | – | 92 (44.7) | |
High |
–
| 81 (41.8) | – | 69 (33.5) | 0.14 |
Weight (kg) | 202 | 26.9 (5.6)
b
| 208 | 25.3 (5.8) | 0.030 |
Height (cm) | 202 | 130.0 ± 5.4 | 208 | 127.6 ± 5.5 | 0.002 |
BMI (kg/m2) | 202 | 15.8 (2.4) | 208 | 15.6 (2.2) | 0.52 |
BMI z score
c
| 202 | 0.092 ± 1.2 | 208 | −0.078 ± 1.0 | 0.19 |
Birth weight (g) | 199 | 3628 ± 565 | 205 | 3475 ± 533 | 0.018 |
Sleep duration (h/night) | 202 | 9.6 ± 0.5 | 208 | 9.7 ± 0.5 | 0.45 |
Breakfast (n (%) every day) | 197 | 166 (84.3) | 204 | 179 (87.7) | 0.42 |
Daily meals (n (%) three/d) | 197 | 83 (42.1) | 204 | 75 (36.8) | 0.37 |
Daily snacking (n (%)) | 197 | 204 | |||
<2 snacks |
–
| 25 (12.7) | – | 31 (15.2) | |
2–3 snacks |
–
| 128 (65.0) | – | 117 (57.4) | |
>3 snacks |
–
| 44 (22.3) | – | 56 (27.5) | 0.63 |
Energy intake (kJ/day) | 197 | 7205 ± 1314 | 204 | 6423 ± 1154 | <0.001 |
Fat intake (g/day) | 197 | 58 ± 15 | 204 | 51 ± 14 | 0.002 |
Maternal BMI (kg/m2) | 187 | 23.5 (5.0) | 201 | 23.7 (4.7) | 0.84 |
Paternal BMI (kg/m2) | 181 | 26.2 (4.1) | 186 | 25.8 (4.9) | 0.32 |
Parameter | Boys (n = 202) | Girls (n = 208) |
p for sex difference |
---|---|---|---|
Sedentary time (min/day) | 367.2 ± 114.4a
| 372.4 ± 118.4 | 0.69 |
Light PA (min/day) | 370.6 ± 83.4 | 400.3 ± 93.4 | 0.035 |
Moderate PA (min/day) | 102.3 (76.2)
b
| 74.4 (59.1) | <0.001 |
Vigorous PA (min/day) | 8.6 (20.5) | 1.9 (6.3) | <0.001 |
PAEE (kJ/kg/day) | 99.3 ± 31.4 | 85.5 ± 25.9 | 0.001 |
Fat mass index (kg/m2) | 2.4 (2.0) | 3.2 (1.9) | <0.001 |
Trunk fat mass index (kg/m2) | 0.9 (0.8) | 1.3 (0.9) | 0.001 |
Fat-free mass index (kg/m2.5) | 11.3 ± 0.7 | 10.5 ± 0.7 | <0.001 |
CRF (W/kg FFM) | 3.8 ± 0.5 | 3.6 ± 0.5 | <0.001 |
3.2 Cumulative Intensity Analyses
3.3 Categorical Analyses and Isotemporal Substitution Models
FMI (% difference, kg/m2) | TFMI (% difference, kg/m2) | FFMI (kg/m2.5) | CRF (W/kg FFM) | |||||
---|---|---|---|---|---|---|---|---|
β (95% CI) |
p
|
β (95% CI) |
p
|
β (95% CI) |
p
|
β (95% CI) |
p
| |
Model 1 | ||||||||
Sedentary time |
1.8 (1.3 to 2.3)
|
<0.001
|
2.1 (1.5 to 2.7)
|
<0.001
| −0.0013 (−0.0085 to 0.0059) | 0.71 | −0.0039 (−0.0083 to 0.00063) | 0.086 |
Light PA |
−1.6 (−2.2 to −1.0)
|
<0.001
|
−1.9 (−2.6 to −1.2)
|
<0.001
| −0.0004 (−0.010 to 0.0095) | 0.93 | −0.0038 (−0.010 to 0.0024) | 0.21 |
Moderate PA |
−3.7 (−4.7 to −2.7)
|
0.002
|
−4.3 (−5.5 to −3.0)
|
<0.001
| 0.0097 (−0.0051 to 0.025) | 0.18 |
0.023 (0.015 to 0.031)
|
<0.001
|
Vigorous PA |
−14.4 (−20.3 to −8.2)
|
<0.001
|
−16.2 (−23.4 to −8.4)
|
0.001
| −0.018 (−0.082 to 0.045) | 0.55 |
0.12 (0.059 to 0.18)
|
0.001
|
PAEE |
−8.0 (−9.8 to −6.2)
|
<0.001
|
−9.2 (−11.4 to −6.9)
|
<0.001
| 0.0087 (−0.017 to 0.034) | 0.48 |
0.046 (0.027 to 0.064)
|
<0.001
|
Model 2 | ||||||||
ST → light PA |
−1.2 (−1.8 to −0.64)
|
0.001
|
−1.5 (−2.1 to −0.82)
|
<0.001
| −0.0026 (−0.013 to 0.0079) | 0.61 | −0.0038 (−0.010 to 0.0027) | 0.23 |
ST → moderate PA |
−1.7 (−2.7 to −0.78)
|
0.002
|
−2.0 (−3.2 to −0.83)
|
0.003
| 0.016 (−0.0002 to 0.031) | 0.052 |
0.014 (0.0064 to 0.022)
|
0.002
|
ST → vigorous PA |
−11.8 (−17.4 to −5.8)
|
0.001
|
−13.1 (−20.1 to −5.5)
|
0.003
| −0.042 (−0.12 to 0.033) | 0.25 |
0.098 (0.040 to 0.16)
|
0.003
|
Light → moderate PA | −0.51 (−1.7 to 0.73) | 0.39 | −0.58 (−2.0 to 0.86) | 0.40 | 0.018 (−0.0042 to 0.041) | 0.10 |
0.018 (0.0054 to 0.031)
|
0.009
|
Light → vigorous PA |
−10.7 (−16.2 to −4.8)
|
0.002
|
−11.8 (−18.8 to −4.3)
|
0.005
| −0.039 (−0.11 to 0.034) | 0.27 |
0.10 (0.046 to 0.16)
|
0.002
|
Moderate → vigorous PA |
−10.2 (−16.4 to −3.5)
|
0.006
|
−11.3 (−19.0 to −2.9)
|
0.013
| −0.057 (−0.14 to 0.024) | 0.15 |
0.083 (0.024 to 0.14)
|
0.01
|