Background & aims: Physical activity (PA) is a major determinant of obesity. Accelerometers have been reported to provide valid measures among adults. However, studies among preschoolers rarely report positive findings. To assess the day-to-day variability of accelerometers in preschoolers.
Methods: Uni-axial accelerometer (Actigraph monitor AM 7164-2.2) counts including one weekend from the time of getting up in the morning until bedtime.
Results: On average, boys showed 899 counts per minute (cpm) compared to 764 for girls (p<0.01; overall mean 828 cpm). Intra-individual correlation for accelerometry data between single days of examination was low with Pearson correlation coefficients between r=0.31 and 0.51. Furthermore, child's body mass index (BMI) and accelerometer measures were not related to each other (Pearson's correlation coefficient r=-0.06). Subsequent analyses showed higher measures (+50%cpm; p<0.01) for instruments placed in front of the umbilicus compared to instruments placed at the right hip.
Conclusions: Measurements of uni-axial accelerometers showed a low reliability among preschoolers. Uni-axial accelerometers placed on elastic belts might measure PA with low precision among preschoolers under free-living conditions possibly due to slipping instruments. This might explain lacking findings of an association between PA and obesity in studies among preschoolers.