title: Longitudinal changes in physical functional performance among the oldest old: insight from a study of Swedish twins.
abstract: OBJECTIVE
  The primary purpose was to characterize mean and individual-level patterns of change in physical functional performance over eight years (2 year intervals) in a community dwelling sample of Swedish twins (579 men and women aged 79-96 years at baseline).
  
  
  RESULTS
  Mixed linear models revealed linear rates of decline for handgrip strength (grip) and time to complete five chair stands, and accelerating decline for peak expiratory flow rate (PEFR) for both sexes. Significant random effects were found for intercept and time for grip and PEFR tests, indicating differences between participants initially and over time. Individual differences in chair-stand performance were significant for initial status only. Age at baseline was predictive of initial status in grip, PEFR and chair performance (women only), but not rate of change. Measures of body size at baseline were predictive of individual variation in initial grip (height), PEFR (weight in men, height in women), and chair performance (height), but had less consistent associations with changes in test performance over time. In the deceased sub-sample (85% of participants), having been further from death was related to less steep declines in grip, but not PEFR or chair performance. Twins from the same pair were related in initial status (twin level variance ~30-70%), but they were not generally related in rate of change.
  
  
  CONCLUSIONS
  These results indicate that changes in physical functional performance in an elderly, community-dwelling population vary across individuals in a testand sex-dependent manner. Constitutional variables (age, sex, body size) are predictive of baseline performance, but explain little variance in change over time. Initial status and rate of change in grip strength had the strongest association with proximity from death, indicating that while PEFR and repeated chair stand time are useful tests to assess function, grip strength appears to be a particularly useful biomarker in the oldest-old.
authors.affiliation: Department of Kinesiology, Pennsylvania State University, University Park, PA 16802, USA. dnp3@psu.edu
authors.forename: David N
authors.initials: DN
authors.lastname: Proctor
authors.forename: Elizabeth B
authors.initials: EB
authors.lastname: Fauth
authors.forename: Lesa
authors.initials: L
authors.lastname: Hoffman
authors.forename: Scott M
authors.initials: SM
authors.lastname: Hofer
authors.forename: Gerald E
authors.initials: GE
authors.lastname: McClearn
authors.forename: Stig
authors.initials: S
authors.lastname: Berg
authors.forename: Boo
authors.initials: B
authors.lastname: Johansson
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001827:Body Height; D001835:Body Weight; D005260:Female; D018737:Hand Strength / Q000502:physiology; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D035002:Lower Extremity / Q000502:physiology; D008168:Lung / Q000502:physiology*; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D010366:Peak Expiratory Flow Rate / Q000502:physiology; D012737:Sex Factors; D013548:Sweden; D014427:Twins / Q000502:physiology*