title: Comparison of pedometer and accelerometer measures of free-living physical activity.
abstract: OBJECTIVE
  The purpose of this investigation was 1) to evaluate agreement between dual-mode CSA accelerometer outputs and Yamax pedometer outputs assessed concurrently under free-living conditions; 2) to determine the relationship between pedometer-steps per day and CSA-time spent in inactivity and in light-, moderate-, and vigorous-intensity activities; and 3) to identify a value of pedometer-steps per day that corresponds with a minimum of 30 CSA-min x d(-1) of moderate ambulatory activity.
  
  
  METHODS
  Data were analyzed from 52 participants (27 men, 25 women; mean age = 38.2 +/- 12.0 yr; mean BMI = 26.4 +/- 4.5 kg x m(-2)) who were enrolled in the International Physical Activity Questionnaire study and wore both motion sensors during waking hours for 7 consecutive days.
  
  
  RESULTS
  Participants averaged 415.0+/-159.5 CSA-counts x min(-1) x d(-1), 357,601 +/- 138,425 CSA-counts x d(-1), 11,483 +/- 3,856 CSA-steps x d(-1), and 9,638 +/- 4,030 pedometer-steps x d(-1). There was a strong relationship between all CSA outputs and pedometer outputs (r = 0.74-0.86). The mean difference in steps detected between instruments was 1845+/-2116 steps x d(-1) (CSA > pedometer; t = 6.29, P < 0.0001). There were distinct differences (effect sizes >0.80) in mean CSA-time (min x d(-1)) in moderate and vigorous activity with increasing pedometer-determined activity quartiles; no differences were noted for inactivity or light activity. Approximately 33 CSA-min x d(-1) of moderate activity corresponded with 8000 pedometer-steps x d(-1).
  
  
  CONCLUSIONS
  Differences in mean steps per day detected may be due to differences in set instrument sensitivity thresholds and/or attachment. Additional studies with different populations are needed to confirm a recommended number of steps per day associated with the duration and intensity of public health recommendations for ambulatory activity.
authors.affiliation: Department of Exercise and Wellness, Arizona State University East, 7001 E. Williams Field Road, Mesa, AZ 85212, USA. Tudor-Locke@asu.edu
authors.forename: Catrine
authors.initials: C
authors.lastname: Tudor-Locke
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Ainsworth
authors.forename: Raymond W
authors.initials: RW
authors.lastname: Thompson
authors.forename: Charles E
authors.initials: CE
authors.lastname: Matthews
mesh_terms: D000054:Acceleration; D000328:Adult; D000367:Age Factors; D015992:Body Mass Index; D017079:Exercise Tolerance / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory; D009043:Motor Activity / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D013022:South Carolina; D013223:Statistics as Topic; D011795:Surveys and Questionnaires; D016138:Walking / Q000502:physiology