title: Critical periods in the variation in body composition in school children.
abstract: OBJECTIVE
  To identify critical periods in the variation in body composition during a school year and determine possible causes.
  
  
  METHODS
  A total of 363 boys and girls aged between 10 and 14 years participated in the study. Before and after the Winter Holidays (WIH) and National Holidays (NAH) (July and September, respectively), measurements were taken of body weight, body fat percentage, waist perimeter, time spent on physical activity and hours of sleep in order to determine the variations. The normality of the data was confirmed and the means were compared with an alpha significance level of p<0.05.
  
  
  RESULTS
  The school children increased in weight by 600 g and 510 g in the NAH and WIH, respectively (p<0.0001), and their body fat percentage was significantly increased during both periods (0.51%); however, the waist perimeter measurement saw no significant changes. It can also be seen that in NAH physical activity dropped by an important amount (-41 min, p<0.0001), though this did not occur in WIH. A significant increase in hours of sleep was also seen during the two holiday periods (~1 to 2 hours/day).
  
  
  CONCLUSIONS
  It is concluded that both NAH and WIH can be considered critical periods due to the sharp increase in body weight and body fat percentage in the school children, where a possible cause is the reduction in time spent on physical activity.
authors.affiliation: Laboratorio de Motricidad Humana, Escuela de Educación Física. Pontificia Universidad Católica de Valparaíso.. carlos.cristi.montero@gmail.com.
authors.forename: Carlos
authors.initials: C
authors.lastname: Cristi-Montero
authors.affiliation: Facultad de Ciencias de la Salud, Universidad Autónoma de Chile.. guilhermebresciani@gmail.com.
authors.forename: Guilherme
authors.initials: G
authors.lastname: Bresciani
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. efi.alvarez@yahoo.es.
authors.forename: Ana
authors.initials: A
authors.lastname: Alvarez
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. valentina_arriagada@hotmail.com.
authors.forename: Valentina
authors.initials: V
authors.lastname: Arriagada
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. beneventi.c@gmail.com.
authors.forename: Angelo
authors.initials: A
authors.lastname: Beneventi
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. valeisidora.canepa@gmail.com.
authors.forename: Valentina
authors.initials: V
authors.lastname: Canepa
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. pauespinoza.vargas@gmail.com.
authors.forename: Paula
authors.initials: P
authors.lastname: Espinoza
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. pelusa_dominio@hotmail.com.
authors.forename: Melisa
authors.initials: M
authors.lastname: Parraguez
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. carlostoledo1990@hotmail.com.
authors.forename: Carlos
authors.initials: C
authors.lastname: Toledo
authors.affiliation: Carrera de Pedagogía en Educación Física, Universidad de Viña del Mar. Valparaíso. Chile.. consuelo_1989_16@hotmail.com.
authors.forename: Consuelo
authors.initials: C
authors.lastname: Valencia
authors.affiliation: Laboratorio de Motricidad Humana, Escuela de Educación Física. Pontificia Universidad Católica de Valparaíso.. rodriguez.investigacion@gmail.com.
authors.forename: Fernando
authors.initials: F
authors.lastname: Rodriguez-Rodriguez
mesh_terms: D000293:Adolescent; D001823:Body Composition; D002648:Child; D005260:Female; D006693:Holidays; D006801:Humans; D008297:Male; D013997:Time Factors