Pedometer accuracy for children: can we recommend them for our obese population?

Abstract

Objective: In this study, we investigated the accuracy of measuring walking steps with commercially available pedometers and an accelerometer-based step-counter in normal and overweight children. Our primary hypothesis was that commercially available pedometers are not an accurate measure of walking steps in normal and overweight children while walking. Our secondary hypothesis was that the accelerometer-based step-counter provides an accurate measure of walking steps in normal and overweight children.

Methods: Thirteen boys (11 +/- 1 years) and 14 girls (11 +/- 1 years) who ranged in BMI from 15 to 27 kg/m(2) (16 normal and 11 overweight or obese) were recruited. Each child wore 4 pedometers at the waist and 1 accelerometer-based step-counter on each ankle. Steps were manually counted and energy expenditure was measured while the child walked on the treadmill at 0.5, 1.0, 1.5, and 2.0 mph, each for 5 minutes. The step-counting devices were also validated while children walked on level ground at a self-selected pace.

Results: For the commercially available pedometers at the lowest speed of 0.5 mph, the percentage error approximated 100% for both of the pedometers. At the fastest speed of 2.0 mph, the percentage error approximated 60%. Conversely the accelerometer-based step-counter showed a percentage error of 24% +/- 22% (mean +/- SD) at 0.5 mph; however, as walking speed increased, the error declined to 5% +/- 8% at 1.0 mph, 4% +/- 5% at 1.5 mph, and 2% +/- 2% at 2.0 mph. The relationship between steps counted and walking energy expenditure showed good linear correlation.

Conclusions: Commercially available pedometers are less accurate for measuring walking and require discretion in their use for children. The accuracy of the accelerometer-based step-counter enables it to be used as a tool to assess and potentially promote physical activity in normal and overweight children.

Figure 1

Pedometer error at the four different walking speeds. Steps were manually counted for all participants (n = 27) while children walked at 0.5, 1.0, 1.5, and 2.0 mph. The manual counts were compared to the steps observed on the pedometers and AS during a 5-minute period. Error is the mean ± SEM at each speed. * Significantly greater error compared to all other speeds, P < 0.0001.

Figure 2

Pedometer error by body category. Steps were manually counted for normal (n = 16) and overweight (n = 11) children. The manual counts were compared to the steps observed on the pedometers and AS during a 5-minute period. Error is the mean ± SEM for all speeds, by weight category. *Significantly greater error in overweight children compared to normal children, P < 0.0001. **Significantly greater error in overweight children compared to lean children, P < 0.0002.

Figure 3

Relationship between manual step counting and energy expenditure. Steps were manually counted (steps/minute) and energy expenditure (kcal/minute) was measured using indirect calorimetry for normal (n = 16) and overweight (n = 11) children. Energy expenditure was adjusted for body weight. Values shown are mean ± SEM.