REPEATABILITY OF ELECTRICALLY-EVOKED EMG SIGNALS IN THE HUMAN VASTUS MEDIALIS MUSCLE

The repeatability of spectral and amplitude parameters and conduction velocity estimates of M-waves was tested on the vastus medialis muscle of 9 normal subjects. Isometric contractions sustained for 30 s were elicited by stimulation of the main muscle motor point and repeated on 5 different days. The initial value and two indicators of myoelectric manifestations of muscle fatigue were computed for each variable. The test-retest Pearson correlation coefficient, the paired Wilcoxon test , and the intraclass correlation coefficient (ICC) showed that paramet ers of spectral variables are more repeatable than those of amplitude variables and conduction velocity, The ICG ranged from 86.4% for the i nitial value of median frequency to 21.6% for the initial value of the average rectified value. Fatigue indices showed ICCs in the range of 20-64%. It is concluded that: (a) initial values and fatigue indices b ased on spectral variables are more repeatable than those based on amp litude variables; (b) the repeatability of conduction velocity estimat es is not yet sufficient for clinical application; (c) M-wave shape, r ather than amplitude or width, is a characteristic of individual muscl es; and (d) electrode location is critical. (C) 1998 John Wiley & Sons , Inc.