title: Twice-weekly, in-school jumping improves lean mass, particularly in adolescent boys.
abstract: OBJECTIVE
  To determine the effect of a twice-weekly, school-based, 10-min jumping regime on muscle and fat tissue in healthy adolescent boys and girls.
  
  
  METHODS
  We replaced regular warm-up activities with jumping in physical education (PE) classes of early high school students for 8 months to observe the effect on muscle and fat tissue. A total of 99 adolescents (46 boys, 53 girls; 13.8 ± 0.4 years) volunteered to participate. Intervention group subjects performed 10 min of varied jumping activity, while control subjects performed a regular PE warm-up. Biometrics, Tanner staging, age of peak height velocity (PHV), vertical jump, whole body lean tissue and fat mass (dual-energy X-ray absorptiometry-derived) were measured at baseline and follow-up. Physical activity was determined by questionnaire.
  
  
  RESULTS
  There were no differences in any measured variable between control and intervention groups at baseline. Boys had a significantly older age of PHV than girls (p = 0.02). No group differences were detected for 8-month change in height, weight or maturity measures for the combined sample; however, at 8 months, jumpers had accrued greater lean tissue mass than controls (p = 0.002). Sex-specific analysis revealed that intervention group boys had gained more lean tissue mass than controls (p = 0.016) and experienced significant fat loss (p = 0.010) than controls, an effect that was not observed in the girls.
  
  
  CONCLUSIONS
  Regular, short-duration, jumping activity during adolescence increased lean tissue mass and boys additionally lost fat mass. Sex-specific and/or maturation-specific factors may explain the disparity in effect.
authors.affiliation: Centre for Musculoskeletal Research, Griffith Health Institute, Griffith University, Gold Coast, Qld, Australia. b.weeks@griffith.edu.au
authors.forename: B K
authors.initials: BK
authors.lastname: Weeks
authors.forename: B R
authors.initials: BR
authors.lastname: Beck
mesh_terms: D015502:Absorptiometry, Photon; D050154:Adiposity; D000293:Adolescent; D000367:Age Factors; D015992:Body Mass Index; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D011446:Prospective Studies; D011793:Queensland; D012572:School Health Services; D012737:Sex Factors; D011795:Surveys and Questionnaires; D013997:Time Factors