ABSTRACT 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.
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