RELATIONSHIPS BETWEEN TRITRAC-R3D VECTORS, HEART-RATE, AND SELF-REPORT IN OBESE CHILDREN

The TriTrac (Professional Products, Inc., Madison, WI) triaxial accele rometer 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 c hildren. Adjusted heart rates were calculated by subtracting preexerci se resting heart rates from heart rates measured in the field. TriTrac and self-reported data were converted to multiples of resting metabol ic rare (METs). Correlations between accelerometer METs and adjusted h eart rates (r = 0.71) were significantly higher (P < 0.001) than corre lations between adjusted heart rates and self-reported METs (r = 0.36) or accelerometer and self-reported METs (r = 0.38). Self-reported MET s 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 ME Ts (2.50 +/- 1.48 vs 1.80 +/- 1.48; P < 0.05) and systematically overe stimated 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 magnitud e score accounted for 69% of the variance in self-reported METs. The v ertical vector did not account for variance in either unadjusted heart rates or self-reported METs. It was concluded that the TriTrac yielde d a better estimate of activity in obese children than self report. In addition, the vector magnitude composite score of the TriTrac account ed for significantly more variance in both self-reported activity and unadjusted heart rates as compared with the vertical directional vecto r of the TriTrac.