An Investigation of Experimentally Induced Central Sensitization and Motor Unit Activity Using High-Density Surface Electromyography Decomposition

Central sensitization (CS) is an amplification mechanism for pain in the central nervous system. I hypothesized that motor unit firing rates in the tibialis anterior would decrease during experimental CS without changes in recruitment thresholds, de-recruitment thresholds, or electromyography amplitude. Two participants were assigned to the “CS” group and received topical application of capsaicin. One participant was randomly assigned to the “placebo” group and a non-noxious cream was applied. Participants dorsiflexed their ankle isometrically and electromyography from the tibialis anterior was collected and decomposed to identify motor units before and after cream application. The mean recruitment thresholds of the CS group were reduced and de-recruitment thresholds and firing rates were unchanged. EMG amplitude in both groups increased. This does not support my hypothesis. I suggest the use of a more advanced decomposition algorithm, larger sample, and more robust controls for psychological factors that influence pain.