Jump-In: Building Better Bones
Condition: Adolescent Development
Study type: Interventional

Summary: 
      The Jump-In study will prospectively assess the effects of impact exercise on skeletal
      development in young girls, including bone mass, bone mineral density, and bone geometry. We
      hypothesize that girls who regularly participate in impact loading exercise will accrue
      greater skeletal mass, increase bone density and undergo structural adaptations that in
      combination will improve bone strength compared to girls who do not participate in impact
      exercise.
    

Detailed description: 
      Jump-In is a school-based, block-randomized, trial of the effects of impact-loading exercise
      on skeletal development in prepubescent and early pubescent girls. Fourth (n=~200) and sixth
      (n=~200) grade girls in 14 Tucson (Arizona) schools with no contraindication to physical
      exercise will be enrolled. Girls in intervention schools will participate in impact
      activities 3 times per week at school, progressively increasing the number (up to 40) of
      jumps and their height (from 6 inches to 18 inches per repetition) over the initial 2 months.
      Thereafter, new activities will be introduced approximately every 2-3 months to maintain
      interest and motivation, and continually stress the skeleton in novel ways, over 2 years of
      intervention. Physical and behavioral assessments will be done in both intervention and
      control groups at baseline, end of the initial school year, and yearly thereafter for 5
      years. Assessments include height and weight, selected skeletal lengths, fat, lean soft
      tissue, bone mineral content and areal density from dual energy x-ray absorptiometry (DXA),
      and bone geometry (e.g., cortical thickness, periosteal circumference and cortical and
      trabecular density) and muscle area from peripheral quantitative computed tomography (pQCT).
      Also, maturation will be assessed via the Tanner Stage (self-assessment against standardized
      drawings of stages of physical development), diet from the Harvard Youth Food Frequency
      Questionnaire, and physical activity using pedometers and standardized questionnaires. We
      hypothesize that girls in intervention schools will demonstrate enhanced skeletal
      development, including greater mineral mass and density, and enhanced bone geometry, leading
      to greater bone strength compared to girls in control schools. We further hypothesize that
      younger (Tanner Stage 1) girls will experience greater adaptations than older girls (Tanner 2
      and 3), and that positive adaptations will be maintained throughout the 3-year follow-up
      period.
    

Intervention name(s): Skeletal loading
Intervention type(s): Other
Intervention description(s): Impact activities, 3 times per week, increasing the number of jumps (up to 40) and increasing height (from 6 inches to 24 inches per repetition) over the initial 8-weeks (2 months). New activities will be introduced approximately every 2-3 months in order to continually stress the skeleton over 2 years.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Basic Science