Preparatory brain activity and anticipatory postural adjustments accompanied by externally cued weighted-rapid arm rise task in non-specific chronic low back pain patients and healthy subjects

OBJECTIVE: Cortical reorganization is one of the most plausible mechanisms underlying impairment of anticipatory postural adjustments (APAs) in low back pain (LBP) patients. In order to clarify changes in corticomotor neurophysiology, APAs were assessed by using electromyography (EMG) and electroencephalography (EEG). METHODS: An equal number (29) of nonspecific LBP patients and healthy subjects performed unilateral rapid arm movements in response to auditory imperative stimulus preceded by warning stimulus within 2 s interstimulus interval. Burst onset activity was calculated in relation to the activity of anterior deltoid for bilateral transverse abdominis/internal oblique (TrA/IO), and also postural muscles on left side, including rectus abdominis, external oblique (E.O), erector spinae and medial head of gastrocnemius (Gc.M). Contingent negative variation (CNV) potentials were recorded by scalp EEG, and the area under receiver operating characteristic curve (AUC) was analyzed. RESULTS: In LBP patients, there was a significant onset delay for E.O and bilateral TrA/IO, but a significant earlier activity for Gc.M (for both P < 0.05). The CNV parameters were considerably greater in LBP patients (P < 0.01). The AUC was significant just for left TrA/IO and E.O muscles (P < 0.05). CONCLUSIONS: The CNV amplitudes were increased, and APA onset times re-organized to be delayed at the trunk and early at the distal limb in LBP cases. These findings support the hypothesis about reorganized activity of cerebral cortex in LBP patients.