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Relationships between TriTrac-R3D vectors, heart rate, and self-report in obese children


Medicine & Science in Sports & Exercise: November 1997 - Volume 29 - Issue 11 - p 1535-1542
Special Communications: Methods

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.

Department of Psychology, University of Texas at El Paso, El Paso, TX; and Departments of Psychology, and Counseling and Educational Psychology, University at Buffalo, Buffalo, NY

Submitted for publication January 1996.

Accepted for publication April 1997.

Request for reprints: Leonard H. Epstein, Ph.D., Behavioral Medicine Laboratory, Psychology Department, Park Hall, University at Buffalo, Buffalo, NY 14260-4110.

Address for correspondence: Karen J. Coleman, Ph.D., Psychology Department, University of Texas at El Paso, El Paso, TX, 79968-0553.

©1997The American College of Sports Medicine