THE RELIABILITY OF MONOPOLAR AND BIPOLAR FINE-WIRE ELECTROMYOGRAPHIC MEASUREMENT OF MUSCLE FATIGUE

Bipolar intramuscular wire electrodes and spectral analysis of the ele ctromyographic signal have been used to measure fatigue in muscles tha t cannot be studied with surface electrodes. Intramuscular electrodes can detect a greater range of frequencies from muscle, obtain a less d istorted signal, and are therefore felt to be more sensitive to detect ing fatigue. To determine the reliability and sensitivity of electrode placement (with a fixed distance) for assessing muscle fatigue, we pl aced three intramuscular electrodes in and two surface electrodes on t he biceps brachii of 30 healthy male subjects. With these electrodes, we devised eight configurations that were analyzed separately for reli ability. Subjects performed four, 30-s isometric fatiguing contraction s divided between two testing sessions. Mean and median frequency of t he power density spectrum were plotted against time. Linear regression was performed to obtain slopes, which were used as indicators of fati gue. The bipolar surface electrode configuration displayed mean and me dian frequency intrasession and mean frequency intersession reliabilit y for slope. All four bipolar fine-wire configurations had mean and me dian frequency intrasession reliability (P less than or equal to 0.05) . Only three of the four bipolar fine-wire configurations approached m ean frequency intersession reliability, and none of the four displayed median frequency intersession reliability. The configuration with dis tal bipolar intramuscular electrodes placed 1 cm apart was the most re liable intramuscular technique. The bipolar fine-wire configurations s tudied showed a trend toward better reliability than monopolar fine-wi re configurations. No intramuscular technique, however, was reliable e nough for clinical use in the study of fatigue.