Measurement of sitting balance using the Manchester Active Position Seat (MAPS): a feasibility study.

Background: Evaluation of the effectiveness of therapy to improve sitting balance has been hampered by the limited number of sensitive objective clinical measures. We developed the Manchester Active Position Seat (MAPS) to provide a portable system to track change in the position of centre of force over time.

Objectives: (1) To investigate whether there is correspondence between the measurement of position change by a forceplate and by MAPS. (2) To explore whether and how MAPS measures changes in position when seated healthy adults change posture.

Design: A feasibility study.

Methods: (1) An adult subject sat on MAPS placed on top of a forceplate. The x and y coordinates of the centre of pressure recorded from the forceplate and centre of force from MAPS during movement were compared graphically. (2) Four adults sat on MAPS using a standardized starting position and moving into six sets of six standardized target postures in a predetermined randomized order. The absolute shift in centre of force from the starting position was calculated.

Results: (1) The pattern of change of position over time was similar for the forceplate and for MAPS although there was a measurement difference, which increased with distance from the centre. (2) The direction of change of position corresponded to the direction of movement to the target postures but the amount of change varied between subjects.

Conclusions: MAPS shows promise as an objective clinical measure of sitting balance, but peripheral accuracy of measurement needs to be improved.