Validating Accelerometry and Skinfold Measures in Youth with Down Syndrome.

Abstract

Current methods for measuring quantity and intensity of physical activity based on accelerometer output have been studied and validated in youth. These methods have been applied to youth with Down syndrome (DS) with no empirical research done to validate these measures. Similarly, individuals with DS have unique body proportions not represented by current methods used to estimate body composition. The purpose of this dissertation was (a) to examine the physical activity patterns in a large sample of youth with DS, (b) to examine the validity of the Actical accelerometer for measuring physical activity and (c) to investigate the accuracy of three published skinfold and anthropometric equations (Lohman, 1987; Slaughter et al., 1988; Kelly & Rimmer, 1987) used to estimate body composition in a sample of youth with DS. A total of 53 participants (27 with DS [15 males], 26 without DS [17 males]), between the ages of 8 and18 years were included in the present study. The Actical accelerometer was validated using a graded treadmill protocol. During the protocol participants wore a portable metabolic system. Heart rate, expired gases, and data counts from the Actical were collected, analyzed, and compared against current thresholds used for determining physical activity intensity. Anthropometric and skinfold measures were compared to results from a criterion measure (Bod Pod ®). Results of this study indicate (a) youth with DS engage in disproportional amounts of sedentary activity and spend very little time in moderate-to-vigorous activity, (b) the Actical ® accelerometer is a valid device for objectively measuring physical activity. However, current cut-points associated with physical activity intensities are likely to underestimate physical activity in youth with DS, and (c) Kelly and Rimmer’s (1987) anthropometric equation demonstrated the most accuracy when compared to the criterion measure. When measuring physical activity and body composition in this sample of youth with DS, considering the unique characteristics of individuals with DS improved measurement accuracy. Based on these results, future research should be directed toward developing population specific methods of measuring and interpreting physical activity and body composition data in a practical way.