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.