Increased neck muscle activity and impaired balance among females with whiplash-related chronic neck pain: a cross-sectional study.

Objective: To investigate neck muscle activity and postural control in patients with whiplash-associated disorder compared with healthy controls.

Design: Cross-sectional study with convenience sampling.

Subjects: Ten females with whiplash-associated disorder (age 37.7 years (21-58), neck pain > 2 years and neck disability index (NDI) > 10) and 10 healthy female controls (age 35.9 years (21-53), NDI < 6).

Methods: Surface electromyography measured muscle activity of the anterior scalene, sternocleidomastoid, neck extensors and upper trapezius muscles, expressed as mean relative activity related to maximum voluntary electromyography (%MVE). On a force plate, 3 balance tasks (Romberg stance with open and closed eyes, 1-legged stance) and a perturbation task with sudden unloading, were performed. The total area, areas from slow and fast components, and range of displacements were calculated from decomposed centre of pressure anterior-posterior and medial-lateral signals.

Results: During balance tasks with closed eyes and one-legged stance, the relative mean activity of all 4 muscles was significantly increased in whiplash-associated disorder compared with healthy controls. Postural sway was also significantly increased.

Conclusion: Increased neck muscle activity and increased postural sway during simple balance tasks indicate disturbed sensory feedback patterns in people with whiplash-associated disorder, which may have negative consequences when performing daily activities.