Sex-specific longitudinal associations between repeatedly measured movement behaviours and adiposity measures in school-aged children: a compositional data analysis approach.

Significant interactions between movement behaviours and sex were observed across all adiposity outcomes in school-aged children.

• 531 children (49.5% girls) were included in the analysis from the GUSTO cohort study.
• Adiposity was assessed at three time points: ages 5.5–6, 7.5–8, and 10–10.5 years.
• Movement behaviours were measured using wrist-worn accelerometers (ActiGraph GT3x).
• Compositional multivariable linear mixed-effect modelling was used to estimate associations.

In girls, higher MVPA relative to other behaviours was associated with lower BMI and lower total abdominal adiposity.

• Higher MVPA was linked to lower BMI of -0.8 (-1.5, -0.1) kg/m² in girls.
• Higher MVPA was linked to lower total abdominal adiposity of -225.5 (-451.6, -2.5) mL in girls.
• These associations were derived from compositional isotemporal substitution models.
• Associations were particularly pronounced for visceral adiposity.

In boys, longer sleep duration relative to other behaviours was associated with lower BMI and lower total abdominal adiposity.

• Longer sleep was associated with lower BMI of -1.6 (-3.2, -0.1) kg/m² in boys.
• Longer sleep was associated with lower total abdominal adiposity of -624.2 (-1225.6, -31.3) mL in boys.
• No corresponding sleep-related benefits were observed in girls.
• Associations were particularly pronounced for visceral adiposity in boys.

Replacing 30 minutes of LPA or SB with MVPA reduced BMI and abdominal circumference by 1–2% and MRI-measured abdominal adiposity by 6–9% in both sexes.

• This finding was derived from the isotemporal substitution model.
• The effect was observed in both boys and girls.
• MRI-derived abdominal adiposity showed stronger associations compared to conventional adiposity indices such as BMI and abdominal circumference.
• The associations were particularly pronounced on visceral adiposity.

Replacing 30 minutes of LPA or SB with sleep reduced BMI and abdominal circumference by 1% and MRI-measured adiposity by 3–6% only in boys, with no significant changes observed in girls.

• This sex-specific finding was derived from the isotemporal substitution model.
• No sleep replacement benefits for adiposity were observed in girls.
• The reduction in MRI-measured adiposity (3–6%) was larger than reductions in BMI or abdominal circumference (1%) in boys.
• These results suggest the need for gender-sensitive approaches in lifestyle interventions.

MRI-derived adiposity measures showed stronger associations with movement behaviours than conventional adiposity indices such as BMI and abdominal circumference.

• Abdominal fat volumes were measured using MRI and compared to BMI and abdominal circumference as adiposity outcomes.
• MRI-measured abdominal adiposity reductions from replacing LPA/SB with MVPA were 6–9%, compared to 1–2% for BMI and abdominal circumference.
• MRI-measured adiposity reductions from replacing LPA/SB with sleep in boys were 3–6%, compared to 1% for BMI and abdominal circumference.
• The paper states that 'stronger associations were observed in MRI-derived measures compared to conventional adiposity indices.'

The study used a compositional data analysis approach to examine 24-hour movement behaviours including MVPA, LPA, sedentary behaviour, and sleep as co-dependent components of a time-use composition.

• Movement behaviours were measured using wrist-worn accelerometers (ActiGraph GT3x) at three time points.
• Compositional multivariable linear mixed-effect modelling was used alongside isotemporal substitution.
• The compositional approach treats MVPA, LPA, SB, and sleep as parts of a 24-hour composition rather than independent variables.
• 531 children aged approximately 5.5 to 10.5 years were followed longitudinally within the GUSTO cohort.