Objective: The objective was to evaluate two accelerometers, the RT3 and the TriTrac-R3D for their ability to produce estimates of physical activity-related energy expenditure (PAEE) in overweight/obese adults.
Research methods and procedures: PAEE estimates from both accelerometers were obtained in two experiments. In Experiment 1, 13 overweight/obese subjects (BMI 34.2+/-6.4 kg/m2) were monitored over 2 weeks in everyday life, PAEE being simultaneously measured by the doubly labeled water method (DLW). In Experiment 2, 8 overweight/obese subjects (BMI 34.3+/-5.0 kg/m2) and 10 normal-weight subjects (BMI 20.8+/-2.1 kg/m2) were monitored during a treadmill walking protocol, PAEE being simultaneously measured by indirect calorimetry.
Results: In Experiment 1, there was no significant difference between methods in mean PAEE (DLW: 704+/-223 kcal/d, RT3: 656+/-140 kcal/d, TriTrac-R3D 624+/-419 kcal/d). The relative difference between methods (accelerometer vs. DLW) was -17.1%+/-16.7% for the RT3 and -20.0+/-44.6% for the TriTrac-R3D. Correlation for PAEE between RT3 and DLW was higher than between TriTrac-R3D and DLW (r=0.67, p<0.05 and r=0.36, p=0.25, respectively). The 95% confidence interval (CI) (kcal/d) of the mean difference between methods was large, amounting to -385 to 145 for the RT3 and -887 to 590 for the TriTrac-R3D. In Experiment 2, both accelerometers were sensitive to the changes in treadmill speed, with no significant difference in mean PAEE between methods in overweight/obese subjects.
Conclusions: Although both accelerometers did not provide accurate estimates of PAEE at individual levels, the data suggest that RT3 has the potential to assess PAEE at group levels in overweight/obese subjects.