Motion discrimination using parameters of bioelectrical impedance

This paper shows results of motion discrimination of wrist joint using four parameters of forearm electrical impedance: Z₀ (resistance when frequency is 0 Hz), Z_∞ (resistance when frequency reaches infinity), f_m (frequency which gives maximum reactance of impedance) and β (ratio of central angle of circular arc to π and degree of distribution of relaxation time). The frequency characteristics of forearm electrical impedance were measured in the following six motions: palmar flexion, dorsi flexion, ulnar deviation and radial deviation of wrist joint, and pronation and supination of forearm. Each flexion angle was 60 deg except ulnarlradial deviation whose angle was 20 deg. Discriminant analysis was used to determine which change ratios of four parameters of forearm electrical impedance with each motion between six motions. As a results of a subject with 60 data, hitting ratio was very high and 95.0%. Two supinations and one radial deviation were mistaken. There were shorter distance between centroid of supination groups and centroid of ulnarlradial deviation groups. When discriminant function calculated using data from a subject was used to determine motions of other subject, the hitting ratio was 70.0%. This was caused by differences of impedance change between subjects in even same motion. Discriminant analysis using parameters of electrical impedance could be motion discrimination.