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Physical Activity and Bone Health
Wendy M Kohrt, PhD University of Colorado Anschutz Medical Campus Department of Medicine, Division of Geriatric Medicine Aurora, Colorado
Physical Activity and Bone Health: Conventional Wisdom, Contemporary Ideas Primer on osteoporosis, bone biology Conventional wisdom – mechanocentric Contemporary ideas – metabolic factors NSAIDs, inflammatory cytokines Disruption of serum calcium homeostasis
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Osteoporosis The major bone disease that is influenced by physical activity Defined by the WHO as a bone mineral density (BMD) 2.5 SD or more below the mean peak BMD of young, healthy adults OR the presence of a fragility fracture
Common Sites of Osteoporotic Fractures
Wrist
Spine Hip
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Facts About Osteoporosis: 20% of those who have a hip fracture die within 1 year and many more need long‐term nursing home care 50% of women and 25% of men over the age of 50 years will have a fracture It is a sneaky disease Overt warning sign: SHRINKING
Trends in Hip Fracture Rate Incidence per 100,000 Men
2000
Men
1800
85+ y
1600 1400 1200 1000 800
75-84 y
600 400
65-74 y
200 0
1986
1990
1994
1998
2002
2006
Year
Adapted from: Brauer CA et al. JAMA 302:1573‐1579, 2009
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Trends in Hip Fracture Rate Incidence per 100,000 Women
3500
Women
3000
85+ y
2500 2000 1500
75-84 y
1000
65-74 y
500 0
1986
1990
1994
1998
2002
2006
Year
Adapted from: Brauer CA et al. JAMA 302:1573‐1579, 2009
Trends in Osteoporosis Medication Use Bisphosphonates
Medication Use, %
20
15
Estrogens
10
5
SERMs
Teriparatide
0
1992
1996
2000
2004
Denosumab
2008
2012
Year
Adapted from: Brauer CA et al. JAMA 302:1573‐1579, 2009
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Pharmacologic Prevention of Hip Fracture Alendronate Risedronate Zoledronic Acid Denosumab Estrogens Raloxifene Teriparatide
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Relative Risk of Hip Fracture Drug vs Placebo Adapted from: Hopkins RB et al. BMC Musculoskeletal Disorders 12:209, 2011
Physical Activity and Hip Fracture Risk Gregson 2010 Robbins 2007 Feskanich 2002 Hoidrup 2001 Boonyaratavej 2001 Farahmand 2000 Gregg 1998 Jaglal 1995 Cummings 1995 Paganini-Hill 1991
Women
Women + Men
Benetou 2011 Wickham 1989
Men Mackey 2011 Michaelsson 2007 Hoidrup 2001 Kujala 2000 Kanis 1999 Mussolino 1998 Paganini-Hill 1991
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Relative Risk of Hip Fracture Most Active versus Least Active
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Prevention of Osteoporosis Strong evidence from RCTs for the anti‐fracture efficacy of several pharmacologic therapies Moderate evidence from observational studies that physical activity reduces risk for hip fracture On average, drugs are more effective at increasing BMD than exercise training
WHY BOTHER PRESCRIBING EXERCISE?
1. Physical activity is a lifelong therapy High
Bone Mass
1
Low
2
3
Physical activity can: Drug therapy 1 increase peak bone mass 2
maintain bone mass
3
attenuate age‐related bone loss
Young
Elderly
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2. Physical activity may be more effective than drugs at increasing bone strength +14%
800
BMC and BMD
5000
Control Risedronate Alendronate
+20%
4000
600
3000
+11%
400
2000
FU and U
1000
+15% 200
1000
0
0
BMC (mg)
BMD (mg/cm2)
U (Nmm)
FU (N)
Adapted from: Mashiba T et al. Bone 28:524, 2001
2. Physical activity may be more effective than drugs at increasing bone strength 2500
2000
94% 5%
60 64%
1500
7% 40
1000
FU and U
BMC and BMD
80
Nonloaded Loaded
20
500
0
0
BMC (mg)
BMD (mg/cm2)
FU (N)
U (mJ)
Adapted from: Turner CH, Robling AG Exerc Sport Sci Rev 31:405, 2003
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3. Physical activity can reduce fall risk physical activity
bone mineral density
balance mobility muscle strength
stronger bones
reduction in falls
reduced risk of fracture
Regulation of Bone Mass by Loading Stress: loading force (N) Strain: deformation resulting from stress (µε) Wolff’s Law: Skeletal tissue responds and adapts to its prevailing mechanical environment Wolff J. Das Gesetz der Transformation der Knochen. Bei Hirschwald, Leipzig, 1892
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Frost’s Mechanostat Theory
50‐200 µε
Low
Strain
F R Bone Gain
Frost, HM. Bone “mass” and the “mechanostat”: A proposal. Anat Rec 219:1–9, 1987
In Vivo Peak Tibia Strain in Humans Jumping, Hopping, Rebounding (max=9096) Jogging, Running, Uphill, Downhill, Stairs (max=5532) Cycling Walking Physiological Window
0
1000
2000
3000
4000
5000
Strain, µε
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Physical Activity and Bone Health: Conventional Wisdom, Contemporary Ideas Primer on osteoporosis, bone biology Conventional wisdom – mechanocentric What types of physical activities have beneficial skeletal effects?
Skeletal Adaptions to Mechanical Loading Key Factors
Site specific High loading intensity Novel strain distribution Few repetitions High strain rate Multiple sessions, rest intervals (not yet evaluated in humans)
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Loading Intensity Change in Bone Mass (%)
60
40
“Although the peak strain magnitude was similar in the natural and artificial loading situations, the position of the neutral axis during artificial loading was rotated approximately 90 degrees.”
20
0
-20 0
1000
2000
3000
4000
Microstrain Adapted from: Rubin CT et al. Calc Tissue Int 37:411, 1985
Change in Bone Mineral Content (%)
Loading Repetitions 150
0 cycles/day 4 cycles/day 36 cycles/day 360 cycles/day
140 130 120 110 100 90 80 0
7
14
21
28
35
42
Time (days)
Adapted from: Rubin CT et al. Bone Joint Surg 66A:397, 1984
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Strain Rate New Bone Volume 3 6 µm x 10
900
*
750 600 450 300 150 0 Low
Moderate
High
Strain Rate Group Adapted from: Mosley JR, Lanyon LE Bone 23:313, 1998
Single vs Multiple Loading Sessions 800
* P < 0.05 vs 360x1
rBFR/BS (µm3/µm2/yr)
*
*
600
400
200
0
0x0
360x1
180x2
90x4
60x6
Adapted from: Robling AG et al. J Bone Miner Res 15:1596‐1604, 2000
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Rest Intervals
Saxon LK et al. Bone 36:454‐464, 2005
BMC Difference Between Limbs (%)
Effects of Increasing, Steady, or Decreasing Loading Forces on Changes in BMC 25 20 15 10 5 0 -5 -10
Control
Adapted from: Schriefer JL et al. J Biomech 38:1838‐1845, 2005
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Current Clinical Recommendations on Physical Activity to Prevent Osteoporosis National Coalition for Osteoporosis & Related Bone Diseases American Society for Bone and Mineral Research National Osteoporosis Foundation
Regular weight‐bearing, balance, and strengthening exercises 2008 Physical Activity Guidelines for Americans Department of Health and Human Services, 2008 http://www.health.gov/paguidelines/Report/pdf
American College of Sports Medicine Position Stand: Physical Activity and Bone Health Med Sci Sports Exerc 36:1985‐96, 2004 Kohrt WM, Bloomfield SA, Little KD, Nelson ME, Yingling VR
Mode: Weight‐bearing endurance and resistance activities Intensity: Moderate to high, in terms of bone‐loading forces Frequency: Weight‐bearing endurance – 3 to 5 days/week Resistance – 2 to 3 days/week Duration: 30 to 60 minutes/day of a combination of weight‐ bearing endurance and resistance activities
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Exercise, HT, and BMD in 60‐ to 72‐yr‐old Women 8 Control HT
Change in BMD (%)
6
Exercise Ex+HT
Main effect of exercise, p