Jf. Nichols et al., Validity, reliability, and calibration of the Tritrac accelerometer as a measure of physical activity, MED SCI SPT, 31(6), 1999, pp. 908-912
Purpose: The purposes of this study were to assess the validity and reliabi
lity of the Tritrac R3D accelerometer during treadmill walking and running
and then to calibrate the instrument. Methods: The Tritrac was assessed on
60 young adults (23.4 +/- 2.9 yr) during treadmill walking and running at 3
.2, 6.4, and 9.7 km.h(-1). The calibration was carried out by identifying r
anges of Tritrac raw data (vector magnitude) values corresponding to light
(2-3.9 MET), moderate (4-7 MET), and vigorous (>7 MET) physical activity. E
nergy expenditure (EE), measured by indirect calorimetry, served as the cri
terion measure. Results: Interinstrument intraclass reliability coefficient
s for Tritracs worn on the right and left hip ranged from 0.73-0.87, while
intersession coefficients demonstrated high reliability for all speeds (R =
0.87-0.92). Paired t-tests comparing mean accelerometer counts at 6.4 km.h
(-1), 0% grade (2647 +/- 456), and 6.4 km.h(-1), 5% grade (2635 +/- 435) de
monstrated no significant difference (P > 0.05). Mean differences between E
E measured by indirect calorimetry and that estimated by the Tritrac ranged
from 0.0082 kcal.kg(-1).min(-1) at 3.2 km.h(-1) to 0.0320 kcal.kg(-1).min(
-1) at 9.7 km.h(-1), with the Tritrac consistently overestimating EE during
horizontal treadmill walking. The relationship between vector magnitude an
d EE across all speeds was highly linear (R-2 = 0.90, SEE = 0.014 kcal.kg(-
1).min(-1)), with little overlap between light, moderate, and vigorous cate
gories. The mean vector magnitudes at 2, 4, and 7 MET were 650, 1772, and 3
455, respectively. Conclusions: These data indicate that the Tritrac is hig
hly reliable from day to day and is sensitive to changes in speed but not g
rade. Furthermore, the Tritrac accurately distinguishes various intensities
of walking and jogging on level ground. With limitations, these cut-points
can be used to categorize light, moderate, and vigorous physical activity
and to estimate EE.