Effect of Task Failure on Intermuscular Coherence Measures in Synergistic Muscles

Figure 1

Experimental setup and data analysis. (a) Experimental setup. Subjects were seated on a leg extension machine in an upright position. They were asked to perform repetitions of a knee extension task until task failure. Surface EMG signals were recorded from three muscles of the quadriceps: rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM). (b) EMG signals were band-pass filtered between 30 and 450 Hz, full-wave rectified, and low-pass filtered with a cutoff frequency of 15 Hz to extract the envelope. (c) Nonnegative matrix factorization algorithm was applied to data for LIE and HIE to reconstruct the activity of the three muscles as a single motor module W containing the relative activation weights of the three muscles as recruited by an activation signal H so that M_r ≈ WxH where M_r is the reconstructed matrix. (d) For the coherence analysis, EMG signals were detrended demodulated by means of Hilbert transform. (e) Then, coherence analysis was performed across the three muscles together (pooled coherence), between pairs of muscles (pairwise coherence) and between pairs of muscles after removing components common to the third muscle (residual coherence).