Comparative interinstrument reliability of uniaxial and triaxial accelerometers in free-living conditions.

The aim of this study was to measure the inter-instrument reliability of the ActiGraph and RT3 accelerometers in free-living conditions. 15 healthy adults wore eight ActiGraph accelerometers and five RT3 accelerometers fastened to their back with an elastic belt and adjustable buckle in free-living conditions. For both accelerometers, the inter-instrument coefficient of variation (CV) decreased with increasing physical activity intensity. The inter-instrument CV of the ActiGraph (3% to 10.5%) was significantly lower than that of the RT3 (12.6% to 35.5%; p < 0.05). This finding demonstrates that the ActiGraph has higher inter-instrument reliability than the RT3. For both accelerometers, the inter-instrument reliability was higher for moderate and vigorous physical activity, the two intensities recommended for public health purposes. Studies using these devices can be compared with a low risk of misclassification of participants who meet the recommendation to perform moderate to vigorous physical activity.