Effects of longer vs. shorter timed movement sequences on alpha motor inhibition when combining contractions and relaxations

Alpha inhibitory processes reflect motor stimuli by either increasing or decreasing amplitude (i.e., power). However, the functional role and interplay of event-related alpha oscillations remains a regulatory domain that has not been sufficiently addressed, particularly with respect to different muscle activation types and durations in consecutive movement (i.e., motor) tasks. The aim of this study was to investigate alpha-band activity (7–13 Hz) in longer vs. shorter timed isometric muscle activations at distinct torques (20% and 40% of maximum voluntary contraction, MVC) when combined in one motor task sequence. In a randomized and controlled design, 18 healthy males volunteered to perform 40 longer (i.e., 6 s) and 40 shorter (i.e., 3 s) motor task sequences, each comprising isometric contractions (i.e., palmar flexion) from baseline to 20% and 40% MVC subsequent to relaxations from 40% and 20% MVC to baseline. Continuous, synchronized EEG, EMG and torque recordings served to determine alpha-band activity over task-relevant motor areas at distinct torques. Main findings revealed increases in alpha activity during subsequent progressive muscle relaxation (from 20% MVC in long and short: p <.001; from 40% MVC in short: p <.05), whereas modulations in relevant motor areas were not significant (p =.84). It may be suggested that an active task-relevant inhibitory process indicates motor task sequence-related relaxation mirrored by an increasing alpha activity.