title: A novel accelerometer-based method to describe day-to-day exposure to potentially osteogenic vertical impacts in older adults: findings from a multi-cohort study.
abstract: This observational study assessed vertical impacts experienced in older adults as part of their day-to-day physical activity using accelerometry and questionnaire data. Population-based older adults experienced very limited high-impact activity. The accelerometry method utilised appeared to be valid based on comparisons between different cohorts and with self-reported activity.
  
  
  
  We aimed to validate a novel method for evaluating day-to-day higher impact weight-bearing physical activity (PA) in older adults, thought to be important in protecting against osteoporosis, by comparing results between four cohorts varying in age and activity levels, and with self-reported PA levels.
  
  
  
  Participants were from three population-based cohorts, MRC National Survey of Health and Development (NSHD), Hertfordshire Cohort Study (HCS) and Cohort for Skeletal Health in Bristol and Avon (COSHIBA), and the Master Athlete Cohort (MAC). Y-axis peaks (reflecting the vertical when an individual is upright) from a triaxial accelerometer (sampling frequency 50 Hz, range 0-16 g) worn at the waist for 7 days were classified as low (0.5-1.0 g), medium (1.0-1.5 g) or higher (≥1.5 g) impacts.
  
  
  
  There were a median of 90, 41 and 39 higher impacts/week in NSHD (age 69.5), COSHIBA (age 76.8) and HCS (age 78.5) participants, respectively (total n = 1512). In contrast, MAC participants (age 68.5) had a median of 14,322 higher impacts/week. In the three population cohorts combined, based on comparison of beta coefficients, moderate-high-impact activities as assessed by PA questionnaire were suggestive of stronger association with higher impacts from accelerometers (0.25 [0.17, 0.34]), compared with medium (0.18 [0.09, 0.27]) and low impacts (0.13 [0.07,0.19]) (beta coefficient, with 95 % CI). Likewise in MAC, reported moderate-high-impact activities showed a stronger association with higher impacts (0.26 [0.14, 0.37]), compared with medium (0.14 [0.05, 0.22]) and low impacts (0.03 [-0.02, 0.08]).
  
  
  
  Our new accelerometer method appears to provide valid measures of higher vertical impacts in older adults. Results obtained from the three population-based cohorts indicate that older adults generally experience very limited higher impact weight-bearing PA.
authors: Musculoskeletal Research Unit, University of Bristol School of Clinical Sciences, Bristol, BS10 5NB, UK.
authors: K
authors: K
authors: Hannam
authors: Musculoskeletal Research Unit, University of Bristol School of Clinical Sciences, Bristol, BS10 5NB, UK.
authors: K C
authors: KC
authors: Deere
authors: Musculoskeletal Research Unit, University of Bristol School of Clinical Sciences, Bristol, BS10 5NB, UK.
authors: A
authors: A
authors: Hartley
authors: Musculoskeletal Research Unit, University of Bristol School of Clinical Sciences, Bristol, BS10 5NB, UK.
authors: E M
authors: EM
authors: Clark
authors: School of Healthcare Sciences, Manchester Metropolitan University, Manchester, M15 6BH, UK.
authors: J
authors: J
authors: Coulson
authors: School of Healthcare Sciences, Manchester Metropolitan University, Manchester, M15 6BH, UK.
authors: A
authors: A
authors: Ireland
authors: MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, SO16 6YD, UK.
authors: C
authors: C
authors: Moss
authors: MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, SO16 6YD, UK.
authors: M H
authors: MH
authors: Edwards
authors: MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, SO16 6YD, UK.
authors: E
authors: E
authors: Dennison
authors: MRC Unit for Lifelong Health and Ageing at UCL, London, WC1E 6BT, UK.
authors: T
authors: T
authors: Gaysin
authors: MRC Unit for Lifelong Health and Ageing at UCL, London, WC1E 6BT, UK.
authors: R
authors: R
authors: Cooper
authors: MRC Unit for Lifelong Health and Ageing at UCL, London, WC1E 6BT, UK.
authors: A
authors: A
authors: Wong
authors: School of Healthcare Sciences, Manchester Metropolitan University, Manchester, M15 6BH, UK.
authors: J S
authors: JS
authors: McPhee
authors: MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, SO16 6YD, UK.
authors: C
authors: C
authors: Cooper
authors: MRC Unit for Lifelong Health and Ageing at UCL, London, WC1E 6BT, UK.
authors: D
authors: D
authors: Kuh
authors: Musculoskeletal Research Unit, University of Bristol School of Clinical Sciences, Bristol, BS10 5NB, UK. Jon.Tobias@bristol.ac.uk.
authors: J H
authors: JH
authors: Tobias
mesh_terms: D061725:Accelerometry / Q000379:methods*; D000368:Aged; D015331:Cohort Studies; D015444:Exercise / Q000502:physiology*; D005260:Female; D015577:Geriatric Assessment / Q000379:methods; D006304:Health Status; D006801:Humans; D008297:Male; D010012:Osteogenesis / Q000502:physiology*; D015203:Reproducibility of Results; D057566:Self Report; D012923:Social Class; D011795:Surveys and Questionnaires; D016138:Walking / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*
keywords: Accelerometry; Bone; Older adults; Physical activity