title: Relationships between TriTrac-R3D vectors, heart rate, and self-report in obese children.
abstract: The TriTrac (Professional Products, Inc., Madison, WI) triaxial accelerometer and diary self report were compared with adjusted heart rates to evaluate 3 d of leisure-time activity in 35 8- to 12-yr-old obese children. Adjusted heart rates were calculated by subtracting preexercise resting heart rates from heart rates measured in the field. TriTrac and self-reported data were converted to multiples of resting metabolic rate (METs). Correlations between accelerometer METs and adjusted heart rates (r = 0.71) were significantly higher (P < 0.001) than correlations between adjusted heart rates and self-reported METs (r = 0.36) or accelerometer and self-reported METs (r = 0.38). Self-reported METs had higher mean standard errors in estimating heart rates (13.93 +/- 6.15 beats.min-1) than did accelerometer METs (10.94 +/- 5.62 beats.min-1; P < 0.001), were significantly greater than accelerometer METs (2.50 +/- 1.48 vs 1.80 +/- 1.48; P < 0.05) and systematically overestimated accelerometer METs. The anteroposterior vector accounted for 36%, and the vector magnitude score accounted for 34% of the variance in unadjusted heart rates. The mediolateral vector and vector magnitude score accounted for 69% of the variance in self-reported METs. The vertical vector did not account for variance in either unadjusted heart rates or self-reported METs. It was concluded that the TriTrac yielded a better estimate of activity in obese children than self report. In addition, the vector magnitude composite score of the TriTrac accounted for significantly more variance in both self-reported activity and unadjusted heart rates as compared with the vertical directional vector of the TriTrac.
authors.affiliation: Department of Psychology, University of Texas at El Paso, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Coleman
authors.forename: B E
authors.initials: BE
authors.lastname: Saelens
authors.forename: M D
authors.initials: MD
authors.lastname: Wiedrich-Smith
authors.forename: J D
authors.initials: JD
authors.lastname: Finn
authors.forename: L H
authors.initials: LH
authors.lastname: Epstein
mesh_terms: D002648:Child; D005260:Female; D006339:Heart Rate; D006801:Humans; D008019:Life Style; D008297:Male; D008432:Mathematical Computing; D009765:Obesity; D010809:Physical Fitness; D012655:Self-Evaluation Programs