Counting Steps in Research: A Comparison of Accelerometry and Pedometry

The objective of this study was to assess the validity of the step count functions in Actical accelerometers and activPAL inclinometers, compared with pedome-ter-derived step count data. Firstly, directly observed step counts over 3 treadmill speeds were compared with steps collected from 3 pedometers, accelerometers, and inclinometers in 10 adults. Secondly, step count data were derived from 22 participants who wore a pedome-ter, accelerometer, and inclinometer over 48 hours. Agreement between measurement tools was determined. All monitors appropriately measured steps in the labo-ratory conditions. In free living conditions, the mean percentage differences with pedometer-determined step counts were -7.3% and 7.0% for the Actical and ac-tivPAL monitors, respectively. With the exception of slow walking for the Actical units (ICC < 0.001), acceptable reliability was found within units for all treadmill speeds, and across units during the free living condition. The 95% prediction interval ranges were wide, ranging from -68.8% to 54.2% for the Acticals, and from -39.1% to 53.2% for the activPALs. Step counts gathered from Actical and activPAL units should not be used interchangeably with pedometer-derived step count data.

Body size, physical activity, and exposure to television in preschoolers

Objective: To investigate relationships between preschool-aged children’s body size and physiccal activity, exposure to television (TV), and parental body size. Design and subjects: Cross-sectional study of 80 children (age: 2 - 5 y, 29% overweight or obese), 73 mothers (37% overweight or obese), and 22 fathers (72% overweight or obese), residing in Auckland, New Zealand, between October 2006 and July 2007. Measurements: Body size was determined using waist circumference and body mass index (BMI). Child exposure to TV was assessed by questionnaire (number of household TV sets, presence of TV in the child’s bedroom, mean TV/ movie watching hours on weekdays and weekend days), and physical activity by 7 days of accelerometry. Results: Compared with children of normal weight/underweight mothers (classified by BMI status), the age-adjusted odds of a child being overweight/obese if their mother was over-weight/obese/otherwise was 2.46 (95% CI 1.11, 5.48, P = 0.03). No other associates of child body size were identified. Conclusion: Contributors to overweight and obesity in preschool aged children are complex and likely to exist in multiple facets of young children’s lives. More detailed measurement of TV watching and other sedentary behaviours is needed. An ecological approach to identifying risk factors for increased body size in preschoolers is required.

Demographic variations in discrepancies between objective and subjective measures of physical activity

Demographic effects (sex and parenthood status) on the level of association between self-reported and accelerometer assessed physical activity were examined among a large diverse sample of adults. Participants (N = 1,249, aged 20 - 65 years) wore accelerometers (Actical) for 7 days and completed an interviewer-administered physical activity recall questionnaire (IPAQ- LF) for the same period. Mean daily minutes of moderate physical activity (MPA) and moderate to vigorous physical activity (MVPA) were used in analyses. Linearity between methods was explored by regressing mean minutes of activity and Pearson’s correlations were performed. A weak association between IPAQ-LF and Actical minutes of MPA and MVPA per day was shown for the whole sample (rs = 0.216 – 0.260). The magnitude of association varied between males (rs = 0.265 – 0.366) and females (rs = 0.124 – 0.167), although no obvious variations in associations were evident for parenting status. The IPAQ-LF produced substantially greater variations in estimates of physical activity than that recorded by the Actical accelerometer and large discrepancies between methods were observed at an individual level. Self-report tools provide a poor proxy of overall human movement, particularly among females. Inferences made at an individual level from self-reported data, such as intervention efficacy or health outcomes, may have substantial error.