title: Estimation of the energy cost of physical activity in infancy.
abstract: OBJECTIVE
  To estimate physical activity energy expenditure (AEE) in groups of free living infants in the first year of life.
  
  
  METHODS
  Mixed longitudinal study of 124 healthy infants, using 232 estimations of AEE made between 1.5 and 12 months. Infants studied at more than one time point were treated as new cross sectional data points. Total energy expenditure and body composition were estimated using doubly labelled water. Sleeping metabolic rate was predicted from weight.
  
  
  RESULTS
  AEE increased from 5% of energy intake at 1.5 months to 34% at 12 months. Growth costs declined by 90%, but metabolisable intake by only 20%, over the same period.
  
  
  CONCLUSIONS
  Energy is increasingly diverted from growth to activity during infancy. Values for AEE may aid in estimating energy requirements of groups factorially. Further work is required, however, on individual variability in AEE, and on the effects of disease, hospitalisation, surgery, and malnutrition.
authors.affiliation: Dunn Nutrition Unit, Cambridge.
authors.forename: J C
authors.initials: JC
authors.lastname: Wells
authors.forename: P S
authors.initials: PS
authors.lastname: Davies
mesh_terms: D001823:Body Composition; D001834:Body Water; D003430:Cross-Sectional Studies; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006128:Growth / Q000502:physiology; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male