Modulation of pain-induced neuromuscular trunk responses by pain expectations: a single group study

The purpose of this study was to investigate the alteration of pain-induced neuromuscular trunk responses by expectations in healthy volunteers.

Twenty-three asymptomatic participants performed series of flexion-extension movements in 3 different experimental conditions: innocuous heat stimulation (control) and noxious heat stimulation associated with expectations of low or high pain intensity. These stimuli were administered by a contact thermode placed over the lumbar region (L4 and L5) to assess the modulation of neuromuscular responses and kinematics during the flexion-extension task. Surface electromyography (EMG) of lumbar erector spinae at L2 and L3 and L4 and L5 as well as lumbopelvic kinematic variables were compared across conditions.

Noxious stimulation significantly altered EMG responses but only in full trunk flexion. Interestingly, this alteration was significant only for muscles where noxious stimulation was applied (L4 and L5) and not for the other segment (L2 and L3). Conversely, expectations significantly altered EMG activity at L2 and L3 but not at the segment where noxious stimulation was applied.

These results confirm previous findings and indicate that experimental pain can alter neuromuscular responses during a trunk flexion-extension task. Furthermore, this study suggests that expectations can alter some of these alterations. Future studies should determine whether neuromuscular changes induced by expectations may contribute to the transition from acute to chronic low-back pain.