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This study investigates the relationship between neck muscle coactivation, neck strength and perceived pain and disability in women with neck pain. Surface electromyography (EMG) was acquired from the sternocleidomastoid (SCM) and splenius capitis (SC) muscles of 13 women with chronic neck pain and 10 controls as they performed 1) maximal voluntary contractions (MVC) in flexion, extension and left and right lateral flexion, 2) ramped contractions from 0% to 50% MVC in flexion and extension and 3) circular contractions in the horizontal plane at 15N and 30N force. Higher values of EMG amplitude were observed for the SC (antagonist) during ramped neck flexion and for the SCM during ramped extension in the patient group (P<0.05). The patients displayed reduced values of directional specificity in the surface EMG of the SCM and SC for the circular contractions (P<0.05). The EMG amplitude of SC during cervical flexion was positively correlated with the patients' pain (R² =0.35, P<0.05) and perceived disability (R² 0.53, P<0.01). An inverse correlation was evident between the amount of activation of SC during cervical flexion and strength (R² =0.54, P<0.01). These observations indicate a relationship between alterations in neuromuscular control in patients with neck pain and functional consequences, including impaired motor performance and increased levels of perceived disability., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Objective: To compare the behavior of sternocleidomastoid motor units of patients with chronic neck pain and healthy controls., Methods: Nine women (age, 40.4+/-3.5 yr) with chronic neck pain and nine age- and gender-matched healthy controls participated. Surface and intramuscular EMG were recorded from the sternocleidomastoid muscle bilaterally as subjects performed isometric contractions of 10-s duration in the horizontal plane at a force of 15 N in eight directions (0-360 degrees ; 45 degrees intervals) and isometric contractions at 15 and 30 N force with continuous change in force direction in the range 0-360 degrees . Motor unit behavior was monitored during the 10-s contractions and the subsequent resting periods., Results: The mean motor unit discharge rate depended on the direction of force in the control subjects (P<0.05) but not in the patients. Moreover, in three of the nine patients, but in none of the controls, single motor unit activity continued for 8.1+/-6.1s upon completion of the contraction. The surface EMG amplitude during the circular contraction at 15N was greater for the patients (43.5+/-54.2 microV) compared to controls (16.9+/-14.9 microV; P<0.05)., Conclusions: The modulation in discharge rate of individual motor units with force direction is reduced in the sternocleidomastoid muscle in patients with neck pain, with some patients showing prolonged motor unit activity when they were instructed to rest., Significance: These observations suggest that chronic neck pain affects the change in neural drive to muscles with force direction., (Copyright 2009 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)