Kids are not little adults: what MET threshold captures sedentary behavior in children?
Level 3 - non-randomized controlled study
Cross-sectional physiological validation study comparing classification cutpoints against indirect calorimetry.
PubMed 26271677 · doi:10.1007/s00421-015-3238-1
What was done
A sample of 102 children aged 7–13 years (54 boys, 48 girls) completed 12 activities randomly selected from a pool of 24 activities ranging from sedentary to vigorous intensity. Energy expenditure was measured continuously using a portable indirect calorimetry system (Oxycon mobile). Minute-by-minute VO2 values were converted to adult-METs (using standard 3.5 ml/kg/min) or child-METs (using estimated child resting metabolic rate). Receiver operating characteristic curves were used to evaluate classification accuracy of the standard 1.5 adult-MET threshold, an adjusted 2.0 adult-MET threshold, and a 1.5 child-MET threshold against predetermined activity categories.
What was found
The standard threshold of 1.5 adult-METs had a sensitivity of 4.7% and specificity of 100.0% for detecting sedentary activities. Shifting to a 2.0 adult-MET threshold improved sensitivity to 36.9% while retaining 100.0% specificity. Using child-METs with a 1.5 threshold yielded a sensitivity of 45.1% and specificity of 100.0%.
Why it matters
Applying adult MET cutpoints to children substantially underestimates sedentary time. Adjusting thresholds to 2.0 adult-METs or using child-specific resting metabolic rates improves classification accuracy in pediatric physical activity research.
Limits
Even with adjusted cutoffs, sensitivity remained poor (under 50%), meaning more than half of sedentary activities were still misclassified. The study utilized a simulated free-living laboratory protocol rather than true free-living behavior, and resting metabolic rate for child-MET calculations was estimated rather than directly measured.
Cited by
- partial Sitting still and breathing consumes approximately 3 ml/kg/min of oxygen, while speaking in conversation consumes approximately 11 ml/kg/min.