Professor Jon TobiasAcademic RheumatologyMusculoskeletal Research UnitUniversity of Bristol

National Osteoporosis Society 2016

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Day-to-day levels of higher impact physical activity are positively related to lower limb bone strength in older women: findings from a population based study using accelerometers to

classify impact magnitude

Background

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• Exercise trials suggest that high impacts are beneficial for skeletal health in postmenopausal women (1)

• Cross sectional studies using accelerometers suggest that day-to-day exposure to high impacts is also positively related to hip bone mineral density (BMD) in adolescents (2) and premenopausal women (3)

• Equivalent studies have not been performed in postmenopausal women, including older individuals at risk of osteoporosis

1. M Martyn-St James, BJSM 2009, 43:8982. K Deere et al JBMR 2012, 27:1887)3. A Vainionpaa et al, OI 2006, 17:455

1. To establish whether day-to-day exposure of older women to high vertical impacts, assessed by seven day accelerometer recordings, is positively related to lower limb bone strength

2. To determine whether any relationship with bone strength we find is explained by relationships with BMD or bone size

3. To explore whether exposure to vertical impacts are related to bone turnover markers, and whether these might also contribute to observed associations with bone strength

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Aims

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Bristol

Cohort for skeletal health in Bristol and Avon (COSHIBA): Unselected community-based study population

65-80 year old women recruited to COSHIBA from GP practices (2007-09)

N= 3200

Invited to research clinic (2015) N= 1064

Attended study clinic session (2015) N= 463

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VIBE Clinic Assessments•Accelerometry

•DXA (total body, lumbar spine & hip)

•pQCT (mid-tibia & distal radius)

•Bone formation (P1NP) and resorption (-CTX) markers (from fasting blood samples)

•Short physical performance battery

•Grip strength

•Jumping mechanography

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VIBE Clinic Assessments•Accelerometry

•DXA (total body, lumbar spine & hip)

•pQCT (mid-tibia & distal radius)

•Bone formation (P1NP) and resorption (-CTX) markers (from fasting blood samples)

•Short physical performance battery

•Grip strength

•Jumping mechanography

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Seven day accelerometer recording

• Light weight (~55g) accelerometer worn in custom belt

for seven days, set to 50Hz sampling rate

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Seven day accelerometer recording

• Light weight (~55g) accelerometer worn in custom belt

for seven days, set to 50Hz sampling rate

• Seven day accelerometer trace was subsequently

down-loaded

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Seven day accelerometer recording

• Light weight (~55g) accelerometer worn in custom belt

for seven days, set to 50Hz sampling rate

• Seven day accelerometer trace was subsequently

down-loaded

• Y axis ‘peaks’ identified and categorised into low (0.5-

1.0g), medium (1.0-1.5g) and higher (>1.5g) impacts*

*K Deere et al, JAPA 2016 24:290

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Linear regression analysis•Exposures

• Number of low, medium or higher impacts/week (log transformed)

•DXA outcomes• Total hip BMD• Femoral neck BMD• Hip cross sectional moment of inertia (CSMI)

•Mid-tibial pQCT outcomes• Periosteal circumference• CSMI

•Adjustment• Age, height, fat mass, lean mass, activity in other bands

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Characteristics of participants in final dataset (n=408)

Mean SDAge (years) 76.8 3.0Height (cm) 158.8 6.2Weight (kg) 68.3 12.0

Accelerometer wear time (valid days) 5.4 1.5

Median 25th Centile 75th Centile

Low impacts (0.5-1.0g)/week 8809 4047 16882

Medium impacts (1.0-1.5)/week 345 99 764

Higher impacts (≥1.5g)/week 42 17 106

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Impacts vs Hip DXA

CSMI = cross sectional moment of inertia (mm4)

Beta shows SD change in DXA outcome per doubling in number of impacts per week, adjusted for age, height, fat mass, lean mass, activity in other bands

Low impacts Medium impacts Higher impacts

Beta lower CI upper CI p Beta lower CI upper CI p Beta lower CI upper CI p

Total hip BMD 0.087 -0.030 0.203 0.145 -0.055 -0.158 0.047 0.287 0.030 -0.042 0.101 0.417

Fem neck BMD 0.072 -0.048 0.192 0.237 -0.072 -0.177 0.033 0.180 0.033 -0.041 0.107 0.380

Hip CSMI 0.008 -0.099 0.115 0.882 -0.108 -0.202 -0.014 0.025 0.067 0.001 0.133 0.045

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Impacts vs tibia pQCT

CSMI = cross sectional moment of inertia (mm4)

Beta shows SD change in pQCT outcome per doubling in number of impacts per week, adjusted for age, height, fat mass, lean mass, activity in other bands

Low impacts Medium impacts Higher impacts

Beta lower CI upper CI p Beta lower CI upper CI p Beta lower CI upper CI p

Peri circ -0.002 -0.021 0.018 0.866 -0.007 -0.024 0.010 0.436 0.015 0.003 0.027 0.017

CSMI 0.016 -0.033 0.064 0.524 -0.031 -0.073 0.012 0.159 0.042 0.012 0.072 0.006

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Impacts vs Bone turnover markers

Low Impacts Medium Impacts Higher Impacts

Beta lower CI upper CI p Beta lower CI upper CI p Beta lower CI upper CI p

-CTX ng/l -0.048 -0.206 0.111 0.556 0.027 -0.117 0.171 0.713 0.085 -0.017 0.187 0.103

P1NP ng/l -0.021 -0.172 0.129 0.780 -0.039 -0.174 0.097 0.577 0.127 0.031 0.224 0.010

Beta shows SD change in bone marker per doubling in number of impacts per week, adjusted for age, height, fat mass, lean mass, activity in other bands

Discussion

• Day-to-day exposure of older women to higher vertical impacts is positively associated

with bone strength of the hip and tibia.

• This relationship appears to be explained by alterations in bone size as opposed to

BMD.

• An equivalent positive association was not observed with low or medium impacts.

• Increased rates of bone formation relative to resorption may contribute to these

relationships between higher impacts and bone strength

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Limitations

• Difficulty in inferring causal inferences from cross sectional studies

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Impacts vs tibia pQCT: additional confounder adjustment

Higher Impacts

Model Beta lower CI upper CI pPeriosteal circumference Age, height, fat mass, other bands 0.012 0.000 0.025 0.056

+ Co-morbidities 0.012 0.000 0.025 0.055

+ Social class 0.012 0.000 0.025 0.055

+ Bone active medication 0.014 0.002 0.027 0.028

Cross sectional moment of inertia Age, height, fat mass, other bands 0.037 0.006 0.069 0.020

+ Co-morbidities 0.038 0.006 0.069 0.020

+ Social class 0.037 0.006 0.069 0.021

+ Bone active medication 0.040 0.008 0.072 0.015

Limitations

• Difficulty in making causal inferences from cross sectional studies

• Seven day accelerometer recordings may not fully capture long term patterns of

physical activity

• Since effect sizes were relatively small, the clinical significance of relationships

between higher impacts and bone strength which we observed is unclear

• Participants are likely to represent a relatively healthy sub-population, limiting

generalisability of our observations

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Conclusions

• Habitual levels of higher, but not medium or low, vertical impacts in older women are

positively associated with lower limb bone size and strength.

• Equivalent relationships are not observed for low or medium impacts.

• The benefit of day-to-day physical activity in older women for their skeletal health

appears to be explained by exposure to higher impacts, despite their rarity and the

relatively low g levels used to define these.

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Acknowledgements Kimberly Hannam1

Kevin Deere1

April Hartley1

Usama Al-Sari1

Emma Clark1

William Fraser2

1Musculoskeletal Research Unit, University of Bristol School of Clinical Sciences2University of East Anglia

http://www.bristol.ac.uk/clinical-sciences/research/musculoskeletal/rheumatology/research/vibe/

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