Effect of training status on beta-range corticomuscular coherence in agonist vs. antagonist muscles during isometric knee contractions

Abstract

Antagonist muscle co-activation is thought to be partially regulated by cortical influences, but direct motor cortex involvement is not fully understood. Corticomuscular coherence (CMC) measures direct functional coupling of the motor cortex and muscles. As antagonist co-activation differs according to training status, comparison of CMC in agonist and antagonist muscles and in strength-trained and endurance-trained individuals may provide in-depth knowledge of cortical implication in antagonist muscle co-activation. Electroencephalographic and electromyographic signals were recorded, while 10 strength-trained and 11 endurance-trained participants performed isometric knee contractions in flexion and extension at various torque levels. CMC magnitude in 13-21 and 21-31 Hz frequency bands was quantified by CMC analysis between Cz electroencephalographic electrode activity and all electromyographic signals. CMC was significant in both 13-21 and 21-31 Hz frequency bands in flexor and extensor muscles regardless of participant group, torque level, and direction of contraction. CMC magnitude decreased more in antagonist than in agonist muscles as torque level increased. Finally, CMC magnitude was higher in strength-trained than in endurance-trained participants. These findings provide experimental evidence that the motor cortex directly regulates both agonist and antagonist muscles. Nevertheless, the mechanisms underlying muscle activation may be specific to their function. Between-group modulation of corticomuscular coherence may result from training-induced adaptation, re-emphasizing that corticomuscular coherence analysis may be efficient in characterizing corticospinal adaptations after long-term muscle specialization.

Effect of the phase of force production on corticomuscular coherence with agonist and antagonist muscles

“…The magnitude of the CMC AGO was lower during IFP than during HFP, as already reported by Masakado and Nielsen (), but also during DFP than during IFP. It can be interpreted that the magnitude of the CMC AGO increases with force level (Dal Maso et al., ; Witte et al., ). However, this interpretation fails to explain the difference in the magnitude of the CMC AGO in between IFP and DFP since the average net joint torque produced during these phases was not significantly different.…”

“…The magnitude of the CMC was quantified as the volume under the time‐frequency map of the CMC (Cremoux et al., ; Dal Maso et al., ), with values set to zero where non‐significant correlation between EMG and EEG signals was detected on the wavelet cross‐spectrum (Bigot et al., ). In the [13.00–31.14] Hz frequency band of interest, the magnitude of the CMC was computed over the three phases of force production (IFP, HFP, DFP) and then averaged over the trials.…”

“…Despite their essential role in motor coordination, the cortical mechanisms underlying the regulation of antagonist muscles are not fully understood (Duchateau & Baudry, ). According to recent studies (Cremoux et al., ; Dal Maso et al., ), the magnitude of the CMC with the antagonist muscles (CMC ANTAGO ) is also significant in the “beta” frequency band. For example, during knee isometric contractions, Dal Maso et al.…”

“…The modulation in net joint torque stability could result from an altered control of the activation of agonist and antagonist muscles, respectively, acting in the direction or in the opposite direction of the net joint torque (Basmajian, ). Recent studies showed the involvement of the primary motor cortex (M1) in the regulation of agonist and antagonist muscle activations with the force level (Cremoux, Tallet, Dal Maso, Berton, & Amarantini, ; Dal Maso, Longcamp, & Amarantini, ; Dal Maso, Longcamp, Cremoux, & Amarantini, ). However, M1 involvement in the regulation of agonist and antagonist muscle activations with the phases of contraction remains largely unknown.…”

“…For example, during knee isometric contractions, Dal Maso et al. () showed that the CMC ANTAGO was modulated with the torque level and the motor expertise, as strength‐trained participants exhibited higher magnitude of the CMC ANTAGO in the “beta” band than endurance‐trained participants. These results suggest a specific cortical regulation of all muscle activations according to their function, i.e., agonists or antagonists.…”