Optimum electrode configuration for detection of arm movement using bio-impedance.

A four-channel impedance measurement system, including a two-channel goniometer, to analyse human arm movement, was constructed. Impedances and joint angles were simultaneously measured for wrist and elbow movements. As the impedance changes resulting from wrist and elbow movements depended heavily on electrode placement, the optimum electrode configurations for those movements were determined by searching for high correlation coefficients, large impedance changes and minimum interferences in ten subjects (age: 29 +/- 6 years). The optimum electrode configurations showed very strong relationships between the wrist joint angle and forearm impedance (correlation coefficient= 0.95 +/- 0.04) and between the elbow joint angle and upper arm impedance (correlation coefficient= -0.97 +/- 0.03). Although the measured impedance changes of the wrist (1.1 +/-1.5 ohms) and elbow (-5.0 +/-2.9 ohms) varied between individuals, the reproducibilities of wrist and elbow impedance changes of five subjects were 5.8 +/- 1.8% and 4.6 +/- 1.4% for the optimum electrode pairs, respectively. It is proposed that this optimum electrode configuration would be useful for future studies involving the accurate measurement of arm movements by the impedance method.