Effects of a previous electromyographic examination studied by frequency analysis, muscle biopsy and creatine kinase

Electromyographic (EMG) examinations were performed twice within two weeks in the same 41 muscles of 32 volunteers. Frequency analysis of the EMG signal showed a pathological high-frequency deviation at the second examination in seven (21%) of the muscles re-examined during the first week. Serum creatine kinase values were higher on the third than on the first day in 11 out of 13 individuals, but the values never exceeded the upper normal limit. A further 10 volunteers were investigated by a single EMG examination followed by a single muscle biopsy. No significant abnormalities were found in the specimens. Owing to the frequency spectrum shifts it is recommended that not less than two weeks should elapse between EMG examinations in the same muscle.