Body position can be monitored in 3D using miniature accelerometers and earth-magnetic field sensors.
OBJECTIVE
The study and diagnosis of movement disorders can be improved by monitoring body position simultaneously with the EMG.


METHODS
We developed a monitor of the 3-dimensional (3D) orientation of body parts that can be applied in long-term ambulatory recordings in the daily life of a patient. The 3D sensor combines miniature sensors for earth's gravity and magnetism. It measures 60 x 50 x 10 mm and draws less than 1 mA of current from +/-5 V battery power. The non-horizontal direction of earth magnetism, as well as torque (pronation) of the body part, is corrected mathematically.


RESULTS
This results in a measurement of the 3D orientation of a body part in terms of vertical inclination and horizontal azimuth.


CONCLUSIONS
Calibration measurements indicate that this method is fairly accurate and practically applicable.
Department of Neurology and Clinical Neurophysiology, University Hospital Leiden, The Netherlands. kemp@rullf2.leidenuniv.nl
B
B
Kemp
A J
AJ
Janssen
B
B
van der Kamp
D000054:Acceleration; D004576:Electromyography; D006112:Gravitation; D008280:Magnetics; D008433:Mathematics; D008991:Monitoring, Physiologic / Q000295:instrumentation*; D009949:Orientation / Q000502:physiology; D011187:Posture / Q000502:physiology*