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

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 raper. In addition, the vector magnitude composite scow of the TriTrac accounted for significantly mow variance in both self-reported activity and unadjusted heart rates as compared with the vertical directional vector of the TriTrac.