Gc. Filligoi et F. Felici, Detection of hidden rhythms in surface EMG signals with a nonlinear time-series tool, MED ENG PHY, 21(6-7), 1999, pp. 439-448
The analysis of the surface electromyographic (sEMG) signal is particularly
attractive because it provides relatively easy access to those physiologic
al processes that allow the muscle to generate force and movement. In this
paper, one of the possible applications of recurrence plot strategy to the
analysis of sEMG is described. Recurrence Quantification Analysis (RQA) is
an efficient time-series analysis tool pertaining to the class of non-linea
r dynamics time-domain processing. We analysed sEMG recorded on the biceps
brachii during isometric contraction both at constant (CF) and non constant
force (NCF), For comparison purposes, experimental data were analysed over
epochs of 1 s so that the hypothesis of sEMG stationarity could be accepte
d. The analysis concerned one of the most widely used frequency parameters
(namely the median frequency, MDF) and one parameter (i.e., the percent det
erminism %DET) extracted using the non-linear technique. Our main results a
re: (i) the gross average evaluated for all subjects on %DET data shows a c
omparable variation with respect to MDF throughout the course of CF experim
ents; (ii) %DET seems able to detect motor unit (MU) synchronisation; (iii)
during non constant force experiments, %DET is more effective than MDF in
detecting sEMG changes determined by brisk transients of force output. (C)
1999 IPEM. Published by Elsevier Science Ltd. All rights reserved.