Reliability of physical activity measures from accelerometry among preschoolers in free-living conditions.
OBJECTIVE
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.
Toschke
Julia Anna
JA
Division of Epidemiology, Institute of Social Pediatrics and Adolescent Medicine, Ludwig-Maximilians University of Munich, Munich, Germany.
von Kries
Rüdiger
R
Rosenfeld
Eva
E
Toschke
André Michael
AM
D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008297:Male; D018670:Monitoring, Ambulatory / Q000295:instrumentation / Q000379:methods; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity / Q000209:etiology* / Q000517:prevention & control; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity