The validity and reliability of a novel activity monitor as a measure of walking.

BACKGROUND The accurate measurement of physical activity is crucial to understanding the relationship between physical activity and disease prevention and treatment. OBJECTIVE The primary purpose of this study was to investigate the validity and reliability of the activPAL physical activity monitor in measuring step number and cadence. METHODS The ability of the activPAL monitor to measure step number and cadence in 20 healthy adults (age 34.5+/-6.9 years; BMI 26.8+/-4.8 (mean+/-SD)) was evaluated against video observation. Concurrently, the accuracy of two commonly used pedometers, the Yamax Digi-Walker SW-200 and the Omron HJ-109-E, was compared to observation for measuring step number. Participants walked on a treadmill at five different speeds (0.90, 1.12, 1.33, 1.56, and 1.78 m/s) and outdoors at three self selected speeds (slow, normal, and fast). RESULTS At all speeds, inter device reliability was excellent for the activPAL (ICC (2,1)> or =0.99) for both step number and cadence. The absolute percentage error for the activPAL was <1.11% for step number and cadence regardless of walking speed. The accuracy of the pedometers was adversely affected by slow walking speeds. CONCLUSION The activPAL monitor is a valid and reliable measure of walking in healthy adults. Its accuracy is not influenced by walking speed. The activPAL may be a useful device in sports medicine.