Physical activity monitoring based on accelerometry: validation and comparison with video observation

The objective of this feasibility study is to evaluate the use of the 'Phys ilog' device, an ambulatory physical-activity recorder based on acceleratio n measurement, for the monitoring of daily physical activities. Acceleratio ns measured at the level of the chest and the thigh are recorded by Physilo g over a period of 1 h in five normal subjects. A specially designed studio -like room allowing the performance of most usual activities of everyday li fe is used. A video film synchronised with the Physilog is obtained for eac h subject to check the accuracy of the data derived from Physilog. Based on the analysis of the average and the deviation of the acceleration signal, an algorithm is developed to classify the activities in four categories, i. e. lying, sitting, standing and locomotion. Compared with the video observa tions, the results from the algorithm show an overall misclassification of 10.7%, which is mainly due to confusion between dynamic activities and the standing posture. In contrast, the misclassification between postures is ne gligible. It is concluded that Physilog can be used in the clinical setting for the reliable measurement and long-term recording of most usual physica l activities.