title: The accuracy of the TriTrac-R3D accelerometer to estimate energy expenditure.
abstract: OBJECTIVE
  This study examined the reliability and validity of the TriTrac-R3D triaxial accelerometer to estimate energy expenditure during various modes of exercise.
  
  
  METHODS
  Twenty subjects (age = 21.5+/-3.4 yr; body mass index = 23.3+/-3.6 kg x m(-2)) performed five exercises (treadmill walking, treadmill running, stepping, stationary cycling, and slideboard), with each lasting 20-30 min and workload increased at 10-min intervals. To test the inter-TriTrac reliability, two TriTrac-R3D accelerometers were worn during each exercise period, and to examine validity, a simultaneous measurement of energy expenditure was made using indirect calorimetry (SensorMedics 2900 Metabolic Cart).
  
  
  RESULTS
  Results showed a significant correlation between the two TriTrac-R3D accelerometers during all exercises. The difference in estimated energy expenditure between the two accelerometers during the walking, stepping, and slideboard exercises was less than 1 kcal x min(-1) but statistically significant (P<0.05). There was also a significant correlation between energy expenditure estimated by each of the TriTrac-R3D accelerometers and indirect calorimetry during walking, running, stepping, and slideboard exercise (P<0.05). The interaction of Method x Workload was significant (P<0.05) for each exercise, indicating that the TriTrac-R3D underestimates energy expenditure and that the magnitude of this underestimation increases as workload increases.
  
  
  CONCLUSIONS
  Therefore, energy expenditure estimated via triaxial accelerometry does not increase with increasing workloads. These results suggest that there are limitations to using triaxial accelerometry to quantify energy expenditure.
authors.affiliation: Obesity/Nutrition Research Center and Human Energy Research Laboratory, University of Pittsburgh, School of Medicine, PA 15213, USA. jjakicic@ukans.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Jakicic
authors.forename: C
authors.initials: C
authors.lastname: Winters
authors.forename: K
authors.initials: K
authors.lastname: Lagally
authors.forename: J
authors.initials: J
authors.lastname: Ho
authors.forename: R J
authors.initials: RJ
authors.lastname: Robertson
authors.forename: R R
authors.initials: RR
authors.lastname: Wing
mesh_terms: D000293:Adolescent; D000328:Adult; D001827:Body Height / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D015203:Reproducibility of Results