title: Objective assessment of activity in older adults at risk for mobility disability.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the validity of three objective measures of physical activity (Accusplit Eagle 120 mechanical pedometer (AE120), NL-2000 electronic pedometer, and IDEEA pattern-recognition device) that varied in their levels of sophistication, among older adults at risk for mobility disability. In addition, we examined the potential influences of gait speed and body mass index (BMI) on step count accuracy.
  
  
  METHODS
  Step counts recorded on the three devices were compared against manual step counts made by two investigators as each participant walked 131 m around an indoor track at their preferred walking speed (N=29; 75.8+/-4.2 yr). Gait speed was determined by dividing total distance walked by time to completion. BMI was calculated from height and body mass measurements.
  
  
  RESULTS
  All three devices significantly underestimated steps taken (AE120=22.8+/-53.9 steps; NL-2000=4.0+/-5.8 steps; IDEEA=5.6+/-7.8 steps), but there was no significant difference between devices (P=0.084). Steps counted by the AE120, NL-2000, and IDEEA were significantly correlated with manual step counts (r=0.508, 0.980, and 0.965, respectively; P<or=0.005). However, the AE120 was not clinically acceptable, sharing only 26% common variance with actual steps taken. The accuracy of the three devices was not influenced systematically by either gait speed or BMI.
  
  
  CONCLUSIONS
  Our data show that the AE120 is a poor choice for measuring physical activity in older adults at risk for mobility disability. Both the NL-2000 and IDEEA devices have acceptable measurement qualities; however, the NL-2000 is the more practical of the two for use in either research or clinical practice.
authors.affiliation: Department of Health and Exercise Science, Wake Forest University, Winston-Salem, NC 27109-7868, USA. marshap@wfu.edu
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Marsh
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Vance
authors.forename: Tera L
authors.initials: TL
authors.lastname: Frederick
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Hesselmann
authors.forename: W Jack
authors.initials: WJ
authors.lastname: Rejeski
mesh_terms: D000054:Acceleration; D000368:Aged; D000369:Aged, 80 and over; D004784:Environmental Monitoring / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D009043:Motor Activity; D009657:North Carolina; D040242:Risk Reduction Behavior; D016138:Walking