Validity And Inter-instrument Reliability Of The Actigraph Accelerometer In 3–5 Year Old Children

Abstract

Accelerometers have been used to objectively measure physical activity in several populations. However, the validity and reliability of these instruments has not been well-established in young children. In order to accurately assess activity in this age group, the validity and reliability of accelerometers needs to be examined. PURPOSE The purpose of this study was to examine the correlation between VO2 and Actigraph accelerometer counts for two different accelerometer placements and to examine the reliability between two monitors during structured and unstructured activities. METHODS Thirty children (age = 4.4 ± 0.75, 53% female, 57% African American, BMI = 16.5 ± 2.1) wore a portable metabolic analyzer (Cosmed K4b2; Rome, Italy) and two Actigraph accelerometers (MTI; Fort Walton Beach, FL); one placed at the hip and one placed on the back. The children wore the equipment during rest, three structured activities, and during inside and outside freeplay times. Pearson correlations were used to determine the relationship between VO2 and accelerometer counts, and to determine the inter-instrument reliability. RESULTS The correlation coefficient for the Actigraph at the hip placement was significantly higher (r=0.78; p=0.018) than the back placement (r=0.68) during the rest and structured activities. During freeplay, the correlation between VO2 and counts was r=0.35 for the hip and r=0.45 for the back. During both structured and unstructured activities, the monitors correlated with each other (r=0.73 and 0.78, respectively). CONCLUSIONS Structured and unstructured activities yielded different correlations between VO2 and counts. Most research in this area has been conducted in laboratory settings (structured). It is therefore necessary to further investigate instrument reliability in field settings (unstructured) in this population and others. Supported by an ILSI Research Foundation grant and NIH grant 5R01HD043125.