Interinstrument Reliability of RT3 Accelerometer at Different Levels Of Physical Activity.

Abstract

Accelerometers are validated instrument for assessing physical activity. However their reliability could vary according to the level of physical activity (PA). PURPOSE: To evaluate the interinstrument reliability of RT3 accelerometer at different level of PA. METHODS: Sixty healthy subjects (thirty boys, thirty girls), aged 10-16 years, were recruited to participate in the study. Subjects were worn two accelerometer on the right hip. Accelerometers data were recorded, every minute, during 9 levels of 15-minute physical activity that varied in intensity from sedentary (i.e., TV watching, reading, playing video game) to vigorous (i.e., running on a treadmill at different speed level). Interinstrument coefficient of variation was assessed using the formula CV = standard deviation of the measure × 100/mean of the measure). RESULTS: Interinstrument coefficients of variation (CV) varied from 4%, to 74.1% according to the intensity of physical activity. Indeed, CV was 44% to 74 % in sedentary, 7% to 47% in light activity, 5% to 6% in moderate activity, and 4% for vigorous activity. CONCLUSIONS: The interinstrument reliability of RT3 accelerometers is poor specially for low level of PA and could lead to significant error in assessing PA in sedentary children in usual condition of life. This discrepancy could account for difference in measuring PA in usual condition of life in subject with low physical activity pattern. The poor reliability of the RT3 accelerometer may be explained by the fact that this device has a wide frequency range (2.0- 10.0 Hz), for detecting movement. However, some thresholds for detecting low PA movement could be different among RT3 devices. Some investigations are needed to characterise accurately these discrepancies.