Changes in Physical Activity and Physical Fitness During Adolescence are Associated with Changes in Coronary Heart Disease Risk Factors The Muscatine Growth Study Kathleen F. Janz, Jeffrey D. Dawson

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Physical Activity and Bone Health during
Childhood and Adolescence Critical Periods for
the Preventionof Osteoporosis
Kathleen Janz
Suggested Links (click below)http//consensus.nih
.gov/cons/111/111_intro.htm http//www.connect.ie/
effo/sreports.htm http//www.cdc.gov/nccdphp/dnp
a/bonehealth/index.htm
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Kathleen JanzDepartment of Health and Sports
Studies,University of Iowa, United States of
America

• My work centers on the health aspects of
  physical activity and fitness, particularly
  during childhood and adolescence. Currently, I
  am working on a longitudinal study with
  colleagues from Dentistry, Medicine, and Public
  Health to examine how genetics, diet, and
  physical activity influence bone growth in
  children. A thorough understanding of bone
  development may allow for interventions to
  prevent bone diseases from occurring at the
  earliest possible ages, when such interventions
  are most likely to be effective. Since physical
  activity is a modifiable factor, understanding
  its effects on bone accretion would be
  particularly useful in the construction and
  implementation of disease prevention strategies.

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Learning ObjectivesPhysical Activity and Bone
Health

• To understand the worldwide scope and severity of
  osteoporosis
• To view osteoporosis as a disease with pediatric
  origins
• To understand the bone adaptation process during
  childhood and adolescence
• To appreciate the contribution of physical
  activity as a behavioral determinant of
  childrens bone health

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Performance ObjectivesPhysical Activity and
Bone Health

• To identify the determinants of bone development
  in children and adolescents
• To interpret common bone measures in relationship
  to osteoporotic risk
• To prescribe the most appropriate type of
  activities for strengthening bone in children and
  adolescence

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Osteoporosis

• Most Common Human Bone Disease
• Low Bone Mineral Mass and Structural
  Deterioration
• Susceptibility to Fractures
• Spine, Hip, Wrist

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Osteoporosis Porous Bone
75 Yr Old (Normal) Vs. 47 Yr Old (Osteoporosis)
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Scope and Severity of Osteoporosis

• 30 to 40 Lifetime Risk for Fracture in Women
• 13 Lifetime Risk for Fracture in Men
• Incidence Rates are Increasing
• Developed Countries Higher Rates
• 30 Hip Fractures Do Not Go Home (US)
• 20 Persons with Hip Fractures Die in a Year (US)

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Measuring Bone Mineral Content

• Bone Mineral is Calcium, Phosphate, and Hydroxide
• Dual X-Ray Absorptometry (DXA) Measures Bone
  Mineral Content
• DXA Adjusts Mass for Area (Areal Bone Mineral
  Density or aBMD)

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WHO Areal Bone Mineral Density Categories T
Scores

• Normal Bone Mineral Density1 SD Average, Young,
  White Female
• Low Bone Mineral Density (Osteopenia) 1 to 2.5
  SD Below Average, Young, White Female
• 2 - 3 X Fracture
• Osteoporosis Greater than 2.5 SD Below
• 5 X Fracture

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Healthy Bones?
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Bone Reacts toSystemic and Local Factors

• SystemicSex Hormones, Growth Hormones, Calcium,
  Vit. D, Smoking, Others
• LocalGravitational Forces and Muscular Forces
• Genetic FactorsRace, Body size, Others

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Osteoporosis Originatesduring Childhood

• Level of Bone Mass during Childhood and
  Adolescence Influences Fracture Risk
• Peak Bone Mass Probably Most Important Population
  Factor
• Peak Bone Mass Nearly Complete Teens and Twenties
• 10 Increase Peak Bone Mass May Reduce Fracture
  Risk by 50

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Natural History of Bone

• Childhood New Bone Added Faster than Old Bone
  Removed
• Peak Bone Mass
• Bone Resorption Exceeds Bone Formation
• Rapid Loss Menopause 3-6 yrs

From Kemper, Pediatric Exercise Science
200012198-216.
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Bone Increases Rapidly During Puberty
aBMDg/cm2
Areal bone mineral density gains in femoral neck
during puberty. From Theintz et al., J Clin
Endocrine Metab 1992 751060-1065.
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Physical Activity is Important for Optimizing
Peak Bone Mass

• Muscular ForcesStrength Building
• Gravitational ForcesWeight-bearing
• Intensity (Strain) More Important than Duration

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Bone Responds Best to High Load Activities in
Unusual Patterns

• Site-specific ResponseE.g., Dominant Arms of
  Racquet Sport Players
• Optimal Load Different than Long Duration and Low
  Intensity for Heart Health

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Evidence Supporting Physical Activity as an
Important Behavioral Determinant of Bone
Development
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Total body and femoral neck peak bone mineral
accrual velocity (g/yr) by inactive, average, and
active physical activity groups for girls and
boys. From Bailey et al., J Bone Miner Res
1999 151672-1679.
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Proximal Femur Bone Mineral Content by Vigorous
Activity Quartiles in 5-year-old Children
Adjusted for Age, Weight, Height
12 ? BMCLeast to Most
From Janz et al., Pediatrics 20011071387-93.
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Summary of Observational Studies Examining the
Relationship of Physical Activity to Bone Measures

• Most Report Differences Ranging from 2 to 20
  between Active and Inactive
• Most Study Subjects have been Caucasian
• Only a Few Studies Report Gender Interaction
• Some Evidence for Physical Activity and
  Maturation Interaction
• Problems with DXA

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Summary of Intervention Studies Examining the
Relationship of Physical Activity to Bone Measures

• High-load, Weight-bearing Protocols
• Most Report a Positive Impact of Intervention
• Bone Measures at Proximal Femur Most Consistently
  Associated
• Some Evidence for Physical Activity and
  Maturation Interaction
• Intervention Trials Now using DXA and Other
  Methods

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Physical Activity and Bone Health during
Childhood and Adolescence

• Create a Wide Margin of Safetyby Optimizing Peak
  Bone Mass
• Age-appropriate High Impact Activities
• Combined with Bone Healthy Diet

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Thank You
Contact me at kathleen-janz_at_uiowa.edu http//w
ww.uiowa.edu/hlss/