The primary purpose of this study was to investigate the accuracy of the activPAL physical activity monitor in measuring step number and cadence in older adults. Two pedometers (New-Lifestyles Digi-Walker SW-200 and New-Lifestyles NL-2000) used in clinical practice to count steps were simultaneously evaluated. Observation was the criterion measure. Twenty-one participants (65-87 yr old) recruited from community-based exercise classes walked on a treadmill at 5 speeds (0.67, 0.90, 1.12, 1.33,

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... 1.56 m/s) and outdoors at 3 self-selected speeds (slow, normal, and fast). The absolute percentage error of the activPAL was <1% for all treadmill and outdoor conditions for measuring steps and cadence. With the exception of the slowest treadmill speed, the NL-2000 error was <2%. The SW-200 was the least accurate device, particularly at slower walking speeds. The activPAL monitor accurately recorded step number and cadence. Combined with its ability to identify primary postures, the activPAL might be a useful and versatile device for measuring activity in older adults.