bone biomechanics - aging
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Bone Biomechanics:
Aging
November 13, 2006
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Aging and Bones
Bone mass peaks at age 20
Bone mass and density can be maintained between20-40
Bones start to lose mass and density at age 40
some athletes may keep bone mass to age 50
Loss of bone mass is greatest between 50-60
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Aging and Bones
spine
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Aging and Bones
forearm
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Spine BMD with Age
Aging and Bones
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Bone and Aging
1% loss per year, 2-3% in osteoporosis
Why?
Changes in calcium regulating hormones
Decreased perfusion of bone tissue due to
changes in bone blood flow
Changes in the properties of bone mineral
material
Decrease in the number and metabolic
activity of cells that produce bone
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Changes in Bones with Aging
Bonemass
Age (yrs)
80605040302010
Critical bone mass
70
Males
Females
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Changes in Bones with Aging
Up to age 40
osteoblast activity = osteoclast activity (bone is
absorbed and replaced in a steady state fashion)
Ages 40-50
men, women similar in bone mass, density
After age 50
women may lose 50%or more of cancellous bonemass (post-menopause)
men may lose 25%or more of cancellous bone mass
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Bone and Aging
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Bone and Aging
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Bone and Aging
3 Major Factors lead to bone loss:
Changes in bone-related hormones
Estrogen, testostorone, growth hormone
Dietary deficiencies Low intake of calcium and Vitamin D rich foods
Decreased physical activity
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Hormonal Changes
Menopausal related
Withdrawal of estrogenreduces absorptionof Ca2+in intestine
Calcitonin and Vitamin-D metabolitesdecrease
Regulate Ca2+homeostasis
Increase in parathyroid hormone
Favor resorption of bone rather thanformation
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Hormonal Changes - Treatments
Adding 170mg of Ca2+ daily nearly doubles
bone density over 1yr.
Injection of vitamin D and estrogen showpromise for bone restoration (1991)
Combination of Ca2+,
vitamin D and exercisedecrease bone loss
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Diet
Inadequate levels of Ca2+, vitamins and
mineral in diet
Elderly eat less and dont include calcium rich
foods Lose ability to produce vitamin-D metabolites
from exposure to sun
Important in Ca
2+
utilization in bone
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DietTreatments
Meta-analysis (several studies)
Women who didnt take Ca2+supplements
2% bone loss in early menopause per year
Women who did 0.8% bone loss in early menopause per year
Women should ingest min of Ca2+
1000mg/day
Post-menopausal1500mg/day
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Bone and Aging
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Changes in Bones with Aging
Relative strength after age 40 decreases 4-5%
per 10 years
No change in stiffness with aging Strain to failure after age 40 decreases 8% per 10
years
Energy absorbed to failure decreases 7-8% per10 years
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Aging and Bones
Common sites of fractures
(1) neck of femur (hip)
(2) thoracic vertebrae
(3) distal radius
Cancellous bones
Affected more than
Cortical bone
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Aging and Bone
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Aging and Bones cancellous bone
50 yrs
80 yrs
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Aging and Bones
cortical bone
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Because of the high bone cartilage
content in young bones: lower strength
bones are less stiff
lower energy to failure
large strain to failure
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BONE
Maturation
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Bone Development and Bone Health
Children need regular exercise (especially pre-puberty)
Watch overtraining, high impact sports!
Reduces their risk of osteoporosis
Systemic effect/advantage may be reduced iftraining stopped
ex. soccer: arm vs. leg
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Bone Injuries
Traumatic - single event or lowfrequency
Very Highload(low frequency)
Unusual type of loads One which the skeletal structure isnt
designed to handle.
Combination loads
shear + bending + torsion + compression,etc.
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Bone Injuries
Materials Fatigue - repeated loads
dont give bone chance to recover
Materials fatigue or overuse or "stress fracture"
Very High frequency(moderate to high loads) Nutritional and hormonalfactors increase risk
ex. low Ca2+intake, low estrogen levels
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Bone Injuries
Fractures
avulsion (tensile)Often accompaniestendon and ligament injuries.
spiral (torsion) impacted (compression)
fatigue or stress fracture
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Minimizing Risk of Suffering a Stress
Fracture
Use proper protective equipment (i.e., helmets,footwear, etc.)
Be careful exercising when fatigued
Avoid coming back too soon after an injury
Proper off-season or pre-season training (pre-hab) Avoid switching sports or events without proper
training
Take occasional days off
Start slowly when initiating training
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Stages of Rehabilitation after
Bone FractureWhen bone fractures, soft tissue must absorb
released energy exacerbating damage
Immediate Treatment (RICE)Rest
Ice
Compression
Elevation
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Therapeutics after Fracture
GOAL: quick restoration of normalfunction
Set fracture, limitedimmobilization
Reconditioning
Passive, ROM exercises
Active exercises(involves muscle contractions)
Modhigh reps; low mod intensity
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Rehabilitation after Connective
Tissue Injuries Reconditioning
Increase blood flow
increase mechanical action
Protection of joint cartilage from atrophy, loss
of cushioning decrease scar tissue
Some mechanical stress needed to promotehealing
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Immobilization
Reduces mechanical stress around area ofbone which has suffered fracture
However, plaster and fiberglass casts(non-removable) weaken bone overall
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Immobilization - 8 wks
stres
s
strain
immobilization
normal
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Osteoporosis
Critical reduction in bone mass to the point
that fracture vulnerability increases
Affects cancellous bone more than cortical
bone
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Osteoporosis
A disease characterized by low
bone mass and structural
deterioration of bone tissue,
leading to bone fragility and an
increased susceptibility to
fractures of the hip, spine,and wrist.
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Osteoporosis- Health Implications
55% of the people 50 years of age and older,have low bone mass: risk of developingosteoporosis and related fractures
Often thought of as an older persons disease, itcan strike at any age.
Responsible for more than 1.5 million fracturesannuallyincluding: 300,000 hip fractures 700,000 vertebral fractures 250,000 wrist fractures 300,000 fractures at other sites
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Risk Factors For Osteoporosis
Risk Factor High Risk Low RiskFamily history yes no
Ethnic background Caucasian African-American
Frame size small largeGender female male
Amenorrhea yes no
Menopause early late
Given birth no yesAge over 50 yes no
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Risk Factors For Osteoporosis
Risk Factor High Risk Low RiskWeight underweight overweight
Physical activity sedentary regular
Smoking yes no
Calcium intake low high
Vitamin D intake low adequate
Soft drink intake high low
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Risk Factors For Osteoporosis
Risk Factor High Risk Low RiskFiber intake high moderate
Alcohol intake high low/moderate
Caffeine high low or none
estrogen low normal
parathyroid hormone low normal
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Exercise and Osteoporosis in
Female Athletes??
15 yrs ago: scientist found some young female athleteshad bone loss (osteopenia) in the spine
some had bone mineral content similar to elderly women
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OSTEOPENIA in
Young Female Athletes
Female Athlete Triad (poor nutrition,amenorrhea, bone loss) occurs in small # but significant % of
population of athletes, active instructors
most common in running, gymnastics,aerobics instructors
associated with disturbances in menstrualcycle
Greater reduction in estrogen
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E i d O t i i
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Exercise and Osteoporosis in
Female Athletes
0
20
40
60
80
100
120
140
sedentary
athletes
amenorrheic
athletes
%sedenta
ry
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Intervention for
Female Athlete Triad
If nutrition, low caloric intake, overtraining, andlow % body fat issues are addressed, normal
menstrual cycle usually resumes
Partial recovery of bone mass noted (long-termeffect unknown?)
Intervention for
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Intervention for
Female Athlete Triad
Educationof coaches, athletes to thisproblem while the athletes are teens isabsolutely critical. Improvement - last 10 years - college +
Concern now - teens, youth sports
Luteinizing hormone (LH; pituitary hormone needed forovulation) 6 months before disturbances in menstrualcycle.
Screening/prevention tool???
Blood draws over 24 hours, expensive
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Intervention for Osteoporosis
Prevention - maximize bone growth duringgrowth phase, maintenance phase; some boneloss with age appears inevitable.
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Intervention for Osteoporosis
Exercise - both weight bearing and weight
training; however, avoid overtraining
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Intervention for Osteoporosis
Calcium supplementation Good overall nutrition
Watch out for: yo-yo diets
rapid weight loss Hormone Replacement Therapy
Estrogen: post-menopausal, amenorrheic women
"designer estrogens" - raloxifene (68% reductionin fractures)
calcitonin (nasal spray)
parathyroid hormone
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Studies have shown that a combination of these
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therapies is more effective than one alone against
osteoporosis!
Notelovitz et al.,
1990
Ch i M h i l St
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Changes in Mechanical Stress-
Bone Adaptations
Wolff's Law - Bone remodels according to functionaldemands
Not tested until the 1960s
Exercise as a health therapeutic agent
Spaceflight
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B l i h S fli h
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Bone loss with Spaceflight
Exposure to the spaceflight causes men and women of allages to lose up to 1% of their bone mass per month due todisuse atrophy. (height increases by 2+ in! - swelling ofvertebral discs)
It is not yet clear whether losses in bone mass will continue as
long as a person remains in the microgravity environment or
level off environment or level off in time.
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Comparing Spaceflight and Inactivity
Changes in Spaceflight rapid - similar initially to immobilization.Slower with inactivity, but progressive.
Decreases in loading, growth factors, decrease in osteoblast activity
(decreased formation), increased osteoclast activity (resorption)
Reduced physical activity is characteristic of aging and could well be a
factor in the loss of bone, but researchers have not yet determined
how much of a role disuse plays on Earth.
E i i S
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In order to exercise on thisergometer, the astronautmust be held down withshoulder pads.
Strategies
Compression - Exercises
Vibration
Electrical Stimulation
Vitamin D
Ca2+
Exercise in Space
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Exercise and Bone Health
Wolff's Law - Bone remodels according to functional
demands
Exercise increases mechanical stress and strain,
growth hormone levels which contribute to increasing
bone mass and density
Stronger, stiffer, and able to store more energy
However, overtraining, especially in children and
older adults is counterproductive.
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