Effects of Age, Walking Speed, and Body Composition on Pedometer Accuracy in Children

Article excerpt

The objective of this study was to investigate the effects of age group, walking speed, and body composition on the accuracy of pedometer-determined step counts in children. Eighty-five participants (43 boys, 42 girls), ages 5-7 and 9-11 years, walked on a treadmill for two-minute bouts at speeds of 42, 66, and 90 m x [min.sup.-1] while wearing a spring-levered (Yamax SW-200) and a piezoelectric (New Lifestyles NL-2000) pedometer. The number of steps taken during each bout was also recorded using a hand counter. Body mass index (BMI) was calculated from height and mass, and percentage of body fat (% BF) was determined using hand-to-foot bioelectrical impedance analysis. The tilt angle of the pedometer was assessed using a magnetic protractor. Both pedometers performed well at 66 and 90 m x [min.sup.1], but undercounted steps by approximately 20% at 42 m x [min.sup.-1]. Although age group, BMI, waist circumference, and % BF did not affect pedometer accuracy, children with large pedometer tilt angles ([greater than or equal to] 10[degrees]) showed significantly greater percent bias than those with small tilt angles (< 10[degrees]). We suggest that the style of waistband on the child's clothing is a more important determinant of tilt angle and thus pedometer accuracy than body composition. Our results also indicate that the NL-2000 pedometer provides similar accuracy and better precision than the SW-200 pedometer, especially in children with large tilt angles. We conclude that fastening pedometers to a firm elastic belt may improve stability and reduce undercounting in young people.

Key words: measurement, pediatric, physical activity, step counts

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Widespread increases in childhood overweight and obesity have triggered an upsurge in the promotion of physical activity in young people. In this regard, the use of pedometers to monitor daily step counts offers several advantages over traditional strategies based on time spent in moderate to vigorous physical activity. Increasing the number of steps accumulated each day is a straightforward concept to understand and is nonthreatening for children of all body sizes and physical abilities. For researchers, pedometers provide an objective and cost-effective measure of children's activity that can be easily compared across study populations and time periods. In recent years, a growing number of studies have used pedometers to provide cross-sectional physical activity data (Duncan, Schofield, & Duncan, 2006; Vincent, Pangrazi, Raustorp, Michaud Tomson, & Cuddihy, 2003) and to evaluate activity interventions in children (Pangrazi, Beighle, Vehige, & Vack, 2003; Schofield, Mummery, & Schofield, 2005).

While unable to measure the intensity, frequency, or duration of activity, pedometers provide estimates of overall activity that correlate well with accelerometers (Kilanowski, Consalvi, & Epstein, 1999), heart rate monitors (Eston, Rowlands, & Ingledew, 1998), and observational techniques (Scruggs et al., 2003). However, only two studies have investigated the validity of pedometers for measuring children's steps in a controlled setting. Ramirez-Marrero, Smith, Kirby, Leenders, and Sherman (2002) compared the step counts recorded by a Yamax Digiwalker SW-200 pedometer with observed steps during 2 min of treadmill walking. Their results indicate that the SW-200 performs accurately at speeds of 70 and 90 m x [min.sup.-1], but underestimates steps by an average of 12.9% at a speed of 58 m x [min.sup.-1]. Beets, Patton, and Edwards (2005) conducted a similar study examining the accuracy of the SW-200 pedometer along with three other models: the Walk4Life 2505, the Sun TrekLINQ and the Yamax Digiwalker SW-701. When compared with observed steps, the mean percent bias of all four pedometers was significant at slow walking speeds of 40 and 54 m x [min.sup.-1].

The accuracy of pedometers at different walking speeds may also depend on the age of the child. …