Figure 1.
Schematic illustration of the experimental setup.
Figure 2.
Comparison of force oscillation (A), force power spectral density (B) and EMG amplitude (C) between isometric (black lines) vs. spring (grey lines) contractions in a representative volunteer.
For plot A, mean force values were subtracted from the force signals and force data were low pass filtered (20 Hz).
Figure 3.
Group average of the maximum value (A) and integral beneath the peak (B) of the force power spectral density during isometric (black bars) and contractions against the spring (grey bars), double y axes were used in these plots.
(C) EMG RMS.**p<.01 (paired t-test).
Figure 4.
Grand-average alpha band CMC across all participants in the two experimental conditions.
Figure 5.
Coherence in the alpha band during isometric contractions and contractions against the spring. 5A) Dots indicate the cortico-muscular coherence peak value for each volunteer, obtained from the EMG and the EEG sensor pair with the highest reported value of alpha band coherence during contractions against the spring.
In this graph, when coherence was below significance level, coherence values were reported equal to “0”. 5B) Group average maximal peak coherence across 6 EEG channels in the alpha and beta bands during isometric contractions and contractions against the spring. *Condition effect p<.05; ‡ Interaction effect p<.05 (Two way ANOVA for repeated measures)
Figure 6.
Partial directed coherence grand-averages across all the subjects shows the detection of significant information flow in the EEG to EMG direction (A and B) and the EMG to EEG direction (C and D) over time for isometric (A and C) and spring (B and C) conditions.
Figure 7.
Bar plot comparing average PDC values and standard deviation in the alpha and beta frequency bands for both isometric and compliant sustained contractions.
* p<.05 (paired t-test)