Cervical muscle co-activation in isometric contractions is enhanced in chronic tension-type headache patients

The purpose of the study was to compare the co-activation of cervical agonist and antagonist muscles between people with chronic tension-type headache (CTTH) and healthy controls during brief isometric cervical flexion and extension contractions. Nine women with CTTH and 10 matched controls participated. Surface electromyographic (EMG) signals were detected from the sternocleidomastoid and splenius capitis muscles bilaterally during cervical flexion and extension contractions of linearly increasing force from 0% to 60% of the maximum voluntary contraction (MVC) in 3 s. Sternocleidomastoid and splenius capitis EMG average rectified values (ARV) were estimated at 10% MVC force increments. During cervical extension contraction, sternocleidomastoid (i.e. antagonist muscle) ARV was greater for patients than for controls in the force range 20-60% MVC (P = 0.029). During cervical flexion, the left splenius capitis (i.e. antagonist muscle) ARV was greater for CTTH patients regardless of the force level (P = 0.02). Maximum cervical flexion and extension force was lower for the CTTH patients compared with controls (P = 0.001). In conclusion, women with CTTH demonstrated greater co-activation of antagonist musculature during cervical extension and flexion contractions compared with healthy women. Increased co-activation of antagonist musculature may reflect reorganization of the motor control strategy in CTTH patients, potentially leading to muscle overload and increased nociception.