Changes in cortical activity measured with EEG during a high-intensity cycling exercise

Abstract

This study investigated the effects of a high-intensity cycling exercise on changes in spectral and temporal aspects of electroencephalography (EEG) measured from 10 experienced cyclists. Cyclists performed a maximum aerobic power test on the first testing day followed by a time-to-exhaustion trial at 85% of their maximum power output on 2 subsequent days that were separated by ∼48 h. EEG was recorded using a 64-channel system at 500 Hz. Independent component (IC) analysis parsed the EEG scalp data into maximal ICs. An equivalent current dipole model was calculated for each IC, and results were clustered across subjects. A time-frequency analysis of the identified electrocortical clusters was performed to investigate the magnitude and timing of event-related spectral perturbations. Significant changes (P < 0.05) in electrocortical activity were found in frontal, supplementary motor and parietal areas of the cortex. Overall, there was a significant increase in EEG power as fatigue developed throughout the exercise. The strongest increase was found in the frontal area of the cortex. The timing of event-related desynchronization within the supplementary motor area corresponds with the onset of force production and the transition from flexion to extension in the pedaling cycle. The results indicate an involvement of the cerebral cortex during the pedaling task that most likely involves executive control function, as well as motor planning and execution.

Keywords: electroencephalography; fatigue; locomotion; motor control.

Copyright © 2016 the American Physiological Society.

Figures

Fig. 1.

A: schematic drawing of the experimental setup. Participants were equipped with a tight-fitting 64-channel electroencephalography (EEG) system and several electrodes to record lower limb electromyography (EMG). Cables were securely attached to the subject's back to avoid artifacts due to cable movement. B: the cadence of a representative subject for a complete time-to-exhaustion trial (gray line). The black line shows the cadence when applying a moving average with a window size of 50-pedal revolutions. The dashed line shows the cadence that the participant voluntarily chose to start the trial. The dotted line shows the corresponding cut-off cadence to define task failure. The hatched areas with the horizontal lines depict the time frame corresponding to the fresh and fatigue condition used for the analysis. The shaded gray area corresponds to the last 5% of the trial ultimately prior to task failure. C: the average cadence across all subjects for the fresh and fatigue phase as well as immediately before task failure. *Significant difference compared with the fresh condition (P < 0.01). †Significant difference compared with the fresh and fatigue condition (P < 0.01). rpm, Revolutions per minute.

Fig. 2.

Scalp map projections from the dipole clusters and power spectra for electrocortical sources corresponding to frontal cortex [Brodmann area (BA) 8; top left], supplementary motor area (SMA) (BA 6; bottom left), right parietal cortex (BA 7; top right), and left parietal cortex (BA 39; bottom right). The scale indicates the strength of the cluster average scalp projection to each electrode. The traces indicate the fresh (black) and fatigue (gray) conditions with shaded gray areas indicating the 95% confidence intervals. The MRI images show the dipole clusters in the sagittal and coronal planes. ICs, independent components.

Fig. 3.

A: event-related spectral perturbations (ERSP) plot of BA 6 showing modulations in EEG spectral power throughout the pedaling cycle (x-axis) as a function of frequency (y-axis, log scaled) with light gray and dark gray indicating increased and decreased activity with respect to the average spectrogram, respectively. Left plot shows data for the fresh condition (first 20%), and the middle plot for the fatigue condition (last 20%). The right plot shows the difference (fresh minus fatigue) between the two conditions with any nonsignificant differences set to zero. B: the plots below show the time-dependent brain activation across the pedaling cycle in the α-, β- and low γ-frequency bands. The gray and white areas indicate the down stroke (power production phase) of the right and left leg, respectively. The onset of right down stroke (RDS) and left down stroke (LDS) corresponds to the right and left leg passing the top dead center (TDC) and is indicated by the arrows below the x-axis.

Fig. 4.

Grand average EMG waveforms in the fresh (black) and fatigue (gray) condition for six lower limb muscles. The x-axis shows the crank cycle with zero referring to the TDC. The y-axis shows the EMG activity normalized to the mean activity of each muscle across the pedaling cycle in the fresh condition.