Repeatability of phasic muscle activity: Performance of surface and intramuscular wire electrodes in gait analysis

Abstract Repeatability is an important consideration for gait analysis data that are being used as an adjunct to clinical decision making. An index of repeatability of wave forms over a number of identical cycles. The purpose of this study was to use the variance ratio to assess the repeatability of phasic muscle activity recorded with surface and bipolar imtramuscular wire electrodes during gait on 10 normal subjects. Variance ratios were calculated using rectified and smoothed elctromyographic data recorded simultaneously from the two types of electrodes. Three measures of repeatability (reproducibility, reliability, and constancy—defined as the cycle‐to‐cycle, run‐to‐run, and day‐to‐day repeatability of phasic muscle activity) were used to compare the performance of the two electrode techniques. Results show that the reproducibility and reliability were better for surface elctrodes than for intramuscular wire electrodes, and constancy was good for sufrace elctrodes and poor for intramuscular wire electrodes. Repeatability improved with increasing smoothing window lengths but was better for surface electrodes than wire electrodes, irrespective of the smoothing window. This study indicates that surface electrode data represent a more consistent measure of activity of superficial muscles, if comparisons are to be made between gait data from different test days.