Validation and Comparison of Two Ankle-Mounted and Two Waist-Mounted Electronic Pedometers

The purpose of this study was to validate and compare the accuracy of two ankle- mounted pedometers [StepWatch 3 (SW-3) and Activity Monitoring Pod 331 (AMP)] and two waist-mounted pedometers [New Lifestyles NL-2000 (NL) and Digiwalker SW-701 (DW-701)] under controlled and free-living conditions. The study had three parts: part I: walking on a treadmill at six different speeds, part II: a) evaluation of potential sources of error: leg swinging, heel tapping, and driving a car in city limits, and b) pedaling a stationary cycle ergometer, and part III: wearing pedometers for 24 hours. Ten males and 10 females walked on a motor driven treadmill at various speeds (27, 40, 54, 67, 80, and 107 m^.min^-1). Simultaneously, an investigator determined the actual steps by a hand counter. In a separate trial, participants performed leg swinging, heel tapping, and cycle ergometery to the beat of a metronome. A subset of 10 participants volunteered to drive their cars 6.4 km over a set course in city limits. In part III, a subset of 15 participants volunteered to wear all four pedometers for a 24-hr period. The SW-3 displayed values that were within 1% of actual steps during treadmill walking at all speeds. The other devices underestimated steps at slow speeds but were accurate at 80 m^.min^-1 and above. The SW-3 registered some steps during heel tapping, leg swinging, and cycling, while the AMP was only responsive to leg swinging. For all devices, the number of erroneous steps detected during driving was negligible. Over a 24-hr period the SW-3 recorded higher step counts than the AMP and DW-701 (P <0.05). Ankle- mounted pedometers (especially SW-3) have superior accuracy at slow walking speeds, which could have applications for studying elderly individuals or those with gait impairments. Although waist mounted pedometers have limitations, they have several advantages that make them suitable for behavioral interventions and large population studies.