A useful method for measuring daily physical activity by a three-direction monitor.

The purpose of this study was to investigate whether a three-direction accelerometer is useful for measuring daily physical activity. Physical activity, being an important part of human behavior, may be related to various aspects of health and disease. In this study, the relationship between the intensity of each action and the three-direction accelerometer (Actigraph) output was compared in 10 healthy subjects under free-living conditions. Subjects wore the Actigraph on their non-dominant wrist and filled out a physical activity check list (self-report) throughout the daytime. Daily physical activities were classified into six categories according to different intensities. The differences of the Actigraph output among each of the six categories were significant by the Kruskal-Wallis analysis (p = 0.001). The Actigraph output appeared to correlate highly with the intensity of actions by the Spearman Rank test (r = 0.95, p < 0.05). The Actigraph output was over-estimated while the subjects were typing, driving and being a passenger in a motor vehicle. The Actigraph was shown to be a useful and convenient device for measuring daily physical activity.