Abstract
The purpose of this study was to investigate whether measurement of the surface electromyogram (EMG) reveals a specific quadriceps femoris (QF) recruitment pattern during various activities and whether this pattern is affected by age and QF wasting.
Surface EMG from the rectus femoris (RF1, vastus lateralis (VL) and vastus medialis oblique (VMO) was recorded in 24 subjects (eight young normals, eight healthy elderly and eight 'weak' elderly) during isometric QF activations at 90° and 0° flexion and simple functional activities such as standing from a seated position and stepping up onto a low block. The raw EMG from each muscle during each activity was full-wave rectified and averaged over successive 10 ms periods to produce a running average EMG signal. The recruitment times of the three muscles were determined at the points at which the EMG signal departed from the baseline recorded prior to the activity. A total of 216 measures of muscle recruitment times were made and the differences between recruitment times were analysed to assess whether they were significantly different.
Results within each subject group failed to reveal significant differences, at the p<0.05 level, in the times of recruitment of the three muscles studied during the activities tested. Close visual inspection of both the raw and averaged electromyograms appeared to indicate that VL and VMO are activated almost simultaneously.