title: Direct and indirect measurement of physical activity in older adults: a systematic review of the literature.
abstract: BACKGROUND
  Due to physiological and cognitive changes that occur with aging, accurate physical activity (PA) measurement in older adults represents a unique challenge. The primary purpose of this study was to systematically review measures of PA and their use and appropriateness with older adults. A secondary aim was to determine the level of agreement between PA measures in older adults.
  
  
  METHODS
  Literature was identified through electronic databases. Studies were eligible if they examined the correlation and/or agreement between at least 2 measures, either indirect and/or direct, of PA in older adults (> 65 years of age).
  
  
  RESULTS
  Thirty-six studies met eligibility criteria. The indirect and direct measures of PA across the studies differed widely in their ability to address the key dimensions (i.e., frequency, intensity, time, type) of PA in older adults. The average correlation between indirect and direct measures was moderate (r=0.38). The correlation between indirect and other indirect measures (r=0.29) was weak, while correlations between direct measures with other direct measures were high (real world: r= 0.84; controlled settings: r=0.92). Agreement was strongest between direct PA measures with other direct measures in both real world and laboratory settings. While a clear trend regarding the agreement for mean differences between other PA measures (i.e., direct with indirect, indirect with indirect) did not emerge, there were only a limited number of studies that reported comparable units.
  
  
  CONCLUSIONS
  Despite the lack of a clear trend regarding the agreement between PA measures in older adults, the findings underscore the importance of valid, accurate and reliable measurement. To advance this field, researchers will need to approach the assessment of PA in older adults in a more standardized way (i.e., consistent reporting of results, consensus over cut-points and epoch lengths, using appropriate validation tools). Until then researchers should be cautious when choosing measures for PA that are appropriate for their research questions and when comparing PA levels across various studies.
authors.affiliation: School of Exercise Science, Physical and Health Education and Department of Psychology, University of Victoria, Victoria, B,C, Canada. kkowalsk@uvic.ca
authors.forename: Kristina
authors.initials: K
authors.lastname: Kowalski
authors.forename: Ryan
authors.initials: R
authors.lastname: Rhodes
authors.forename: Patti-Jean
authors.initials: PJ
authors.lastname: Naylor
authors.forename: Holly
authors.initials: H
authors.lastname: Tuokko
authors.forename: Stuart
authors.initials: S
authors.lastname: MacDonald
mesh_terms: D000368:Aged; D015444:Exercise; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans