title: Interunit and intraunit reliability of the RT3 triaxial accelerometer.
abstract: BACKGROUND
  Interest in the quantification of physical activity is on the rise. Triaxial accelerometry has frequently been used; however, research on the reliability of these devices is limited. We examine the interunit and intraunit reliability of 22 RT3 triaxial accelerometers using a performance-documented laboratory agitator.
  
  
  METHODS
  The RT3 units were tested while moving in 2 directions (antero-posterior, medio-lateral) and speeds (150 and 275 RPM) on a shaker with simultaneous documented performance output for three 24-hour periods.
  
  
  RESULTS
  Minimal shaker variance was recorded for all trials (coefficients of variation [CVs] < 0.52%). Our data demonstrate good reliability within RT3s (CVs < 1.81%) but poor reliability among the 22 units (CVs range = 9.5% to 34.7%).
  
  
  CONCLUSIONS
  In longitudinal studies, each subject should use the same RT3 unit at each assessment. The use of multiple RT3 units in cross-sectional studies is not recommended because data interpretation would be compromised by the high between-unit variability.
authors.affiliation: Exercise Physiology and Body Composition Laboratory, Dept of Medicine, University of California at San Francisco, CA 94143, USA.
authors.forename: Joanne B
authors.initials: JB
authors.lastname: Krasnoff
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kohn
authors.forename: Frankie K K
authors.initials: FK
authors.lastname: Choy
authors.forename: Julie
authors.initials: J
authors.lastname: Doyle
authors.forename: Kirsten
authors.initials: K
authors.lastname: Johansen
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Painter
mesh_terms: D000054:Acceleration; D000704:Analysis of Variance; D016552:Ergometry / Q000295:instrumentation*; D006801:Humans; D018670:Monitoring, Ambulatory / Q000295:instrumentation*; D009043:Motor Activity; D015203:Reproducibility of Results