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Longus colli muscle has a significant role in postural control. A reduction of longus colli cross-sectional area (CSA) has been demonstrated in neck pain patients. However, pain-side related difference and its relationship with clinical features and standing balance remain unclear.To investigate side-to-side difference in the longus colli CSA and to determine the relationships of the CSA with clinical characteristics and standing balance in neck pain patients.Cross-sectional study.Fifty participants with chronic non-specific neck pain (20 unilateral and 30 bilateral) were recruited. CSA of the longus colli muscle was measured using ultrasound imaging. Balance was measured using a force platform during a narrow stance with eyes open, eyes closed, and neck torsion (left and right). Balance outcomes were sway area and displacement in anterior-posterior (AP) and medial-lateral (ML) directions. Clinical characteristics were neck pain intensity, disability, and duration.The longus colli CSA was reduced on the painful side in patients with unilateral neck pain (p 0.01). There was a trend towards reduced CSA on the more painful side in those with bilateral neck pain (p = 0.08). The reduced CSA was mostly correlated with the greater AP sway displacement and sway area (r ranged from -0.27 to -0.54, p0.05). The longus colli CSA was not correlated with pain intensity, disability, and duration (p 0.05).The longus colli CSA was reduced on the painful side of neck pain. The reduced CSA was correlated with impaired standing balance, but not with clinical characteristics of neck pain.

To compare neck, trunk, and lower extremity muscle activity in standing in persons with neck pain (NP) to healthy controls and determine associations with postural sway.Participants included 25 persons with NP and 25 controls. Surface electromyography was recorded bilaterally from neck (sternocleidomastoid, SCM; splenius capitis, SC; upper trapezius, UT), trunk (erector spinae, ES), and lower extremity (rectus femoris, RF; biceps femoris, BF; tibialis anterior, TA; medial gastrocnemius, GN) muscles. Postural sway was measured using a force platform in narrow stance with eyes open/closed, on firm/soft surfaces.Compared to controls, the NP group demonstrated higher activity in all muscles, except UT and had higher amplitude ratios for neck muscles (SCM, SC) for all tasks (p .05). No between-group difference was found in amplitude ratios for lower extremity muscles, except for GN. Lower extremity activity was moderately correlated with larger postural sway for both groups (r = 0.41-0.66, p .05). There were no correlations between sway and neck and trunk muscle activity (p .05).Increased muscle activity with NP is associated with increased postural sway. Both groups used similar postural control strategies, but the increased neck activity in the NP group is likely related to the NP disorder rather than postural instability.