Body position can be monitored in 3D using miniature accelerometers and earth-magnetic field sensors

Objectives: 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 60×50×10 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.