Neck Muscle Stiffness is Not Related to Neck Pain

We usually assume that people with chronic neck pain will exhibit increased stiffness of their neck muscles. Manual therapists working with people with chronic neck pain tend to work on loosening those tight neck and shoulder muscles. Recently there is also another view that neck pain may not be related to muscle stiffness. While some studies found increased stiffness of splenius and trapezius muscles in people with neck pain, other studies found similar stiffness between people with and without neck pain. Thus, there is still no clear evidence of whether people with neck pain will demonstrate an increase in neck muscle stiffness. A study led by German scientists compared the stiffness of the neck muscles between women with chronic non-specific neck pain and asymptomatic controls. The study was published in the Journal of Orthopaedic & Sports Physical Therapy.

The study recruited 20 women (median age 50 years) with chronic non-specific neck pain and 18 asymptomatic women. They were asked to perform various tasks: relaxed sitting, isometric neck extension at various forces. 30-degree rotation, prone relaxed, prone head lift, desk stress, sitting with 1 kg sand balanced on the head. Muscle stiffness of neck extensor muscles and surrounding area: trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis and multifidus muscles were measured using an instrument called ultrasound shear wave elastography.

The results showed that women with neck pain showed a reduced neck ROM. However, over all tasks, the average neck muscle stiffness was not significantly different between those with neck pain and the asymptomatic group. Participants with neck pain reported sensations of neck stiffness, but measurements did not show higher muscle stiffness.

The authors further asked the question, “Why do patients feel muscle stiffness?” They hypothesised that the feeling of stiffness during neck movement means that the sensory feedback that is received with the motion does not fit the unconscious expectations. Usually, the sensation of movement does not come into awareness when it fits into the expectations. Stiffness to neck movement may be perceived when there is a delay in movement. The central nervous system may interpret a small delayed neck movement as the result of muscle stiffness. The authors cautioned that the physiology behind the sensation of stiff neck muscles and the complexity of influencing factors is still not well understood.

The authors concluded that muscle stiffness measured using shear wave elastography showed similar muscle stiffness in people with and without chronic neck pain despite the sensation of increased neck stiffness in those with chronic neck pain. They added that manual therapy usually aims to reduce neck muscle tone based on the assumption that perceived neck stiffness corresponds to objective muscle stiffness. The findings from this research question this common assumption.

Figure: Averaged neck stiffness at various positions for participants with neck pain (blue) and without neck pain (green). The box and whisker represents the range of measured values. The line in the box indicates the median of observations, while the whiskers indicate the lower an higher values observed. Figure adapted from Journal of Orthopaedic & Sports Physical Therapy.