Brain-imaging during an isometric leg extension task at graded intensities

Area of Science:

• Neuroscience
• Motor Control
• Exercise Physiology

Background:

• Imaging brain activity during intense physical movements is challenging due to motion and myogenic artifacts.
• Previous research has primarily focused on low-intensity or single-joint exercises, leaving a gap in understanding cortical activation during maximal efforts.

Purpose of the Study:

• To investigate cortical activation patterns during isometric leg extensions of increasing intensity.
• To assess the feasibility of using electroencephalography (EEG) for brain imaging during maximal voluntary contractions.

Main Methods:

• Eleven healthy volunteers performed isometric leg extensions at 20%, 40%, 60%, 80%, and 100% of their maximal voluntary contraction.
• Electroencephalography (EEG) and electromyography (EMG) were recorded simultaneously.
• Standardized low-resolution brain electromagnetic tomography (sLORETA) analyzed cortical current density in motor and somatosensory areas.

Main Results:

• EEG signal quality was sufficient up to 80% maximal intensity; maximal intensity (100%) introduced significant myogenic artifacts.
• Primary motor cortex (M1) showed higher ipsilateral activity, while premotor cortex (PMC), primary somatosensory cortex (S1), and somatosensory association cortex (SAC) exhibited higher contralateral activity.
• Cortical current density in M1 and EMG activity increased with exercise intensity, with M1 showing the highest activation, followed by S1, PMC, and SAC.

Conclusions:

• EEG can effectively record cortical activity during submaximal isometric contractions (up to 80%) but is limited at maximal intensities due to artifacts.
• Isometric leg extensions primarily engage the primary motor cortex (M1), with limited apparent involvement of S1, PMC, and SAC in direct force output.
• Future research should focus on artifact reduction techniques to enable brain imaging during maximal intensity movements.