In-chair movement: validity, reliability and implications for measuring sitting discomfort

Sitting discomfort is traditionally evaluated with subjective rating scales which are referenced to an objective correlate (e.g. sitting posture) meas ured on a static (i.e. non-continuous) basis. Since sitting discomfort is d ynamic in nature, it requires continuous, objective measurement. We therefo re adapted an interface pressure mat to continuously record in-chair moveme nt (ICM) as an indirect measurement of sitting discomfort by tracking the c enter of pressure (COP) at the buttock-chair interface. Here we report on t wo phases in the development of the COP system: laboratory validity and fie ld reliability. In the laboratory study we confirmed system validity by sim ultaneously tracking ICM with the mat and a force platform (r(2) > 0.80) an d by comparing subjects' COP movement with their gross trunk movements (r(2 ) > 0.86). In our field study we used the intraclass correlation coefficien t to establish a data sampling (i.e. selection) protocol that was reliable. We collected ICM data on seated telecommunications Directory Assistance op erators during 2 h field tests. Results showed that using a minimum samplin g time of 5 min and then averaging a series of 5 min samples of ICM was mor e reliable than single discrete samples. Using the averaging protocol, we a lso showed that ICM increased significantly over 2 h and that ICM did not d iffer between trials. (C) 2000 Elsevier Science Ltd. All rights reserved.