Motion pattern and posture: Correctly assessed by calibrated accelerometers

Basic motion patterns and posture can be distinguished by multi-channel accelerometry, as recently shown. A refinement of this methodology appeared to be desirable to further increase its validity, especially to distinguish walking and climbing stairs, and body rotation during sleep. Recordings were made of 31 subjects, according to a standard protocol comprising thirteen motions and postures. This recording was repeated three times with appropriate permutation. Five uni-axial sensors and three sites of placement (sternum with three axes, right and left thigh) were selected. A hierarchical classification strategy used a standard protocol (that is, individual reference patterns) to distinguish subtypes of moving behaviors and posture. The analysis method of the accelerometer signals yielded a reliable detection of 13 different postural and activity conditions (only 3.2 % misclassifications). A minimum set of sensors can be found for a given application, for example, a two-sensor configuration would clearly suffice to differentiate between four basic classes (sitting, standing, lying, moving) in ambulatory monitoring.