Optimum electrode configuration for detection of leg movement using bio-impedance

Impedances and joint angles were simultaneously measured during ankle and knee movements. The correlation coefficients of the joint angle and the impedance change from human leg movement were obtained using an electro-goniometer and a four-channel impedance measurement system. Because the impedance changes resulting from ankle and knee movements depended heavily on the electrode placement, we determined the optimum electrode configurations for those movements by searching for high correlation coefficients, large impedance changes and minimum interferences in ten subjects (age: 20+/-4). Our optimum electrode configurations showed strong relationships between the ankle joint angle and lower leg impedance (correlation coefficient=-0.91+/-0.06) and between the knee joint angle and knee impedance (correlation coefficient=0.94+/-0.04). The reproducibilities of the impedance changes of five subjects due to the ankle and knee were 6.3+/-1.9% and 5.1+/-1.7% for the optimum electrode pairs, respectively. We propose that this optimum electrode configuration would be useful for future studies involving the convenient measurement of leg movements by the impedance method.