It appears that patients with tension-type headache (TTH) have relatively weak neck extension muscles, a new study shows.
Researchers found that these patients are 26% weaker than controls with respect to neck extension muscles, that they have a 12% smaller extension/flexion ratio, and that they have a borderline significant difference in the ability to generate muscle force over the shoulder joint.
“We found that patients with tension-type headache exhibited decreased muscle strength in the neck extensor muscles, which caused this reduced ratio between extension and flexion,” said lead study author Bjarne Madsen, a physiotherapist and PhD student in the Department of Sports Science and Clinical Biomechanics, University of Southern Denmark and Danish Headache Center Glostrup Hospital.
With this reduced ratio, the muscles in the front of the neck pull the head forward, which causes continuous muscular activity in the neck, explained Madsen. “This can lead to pain and, over time, it can cause tension-type headache.”
The study was published April 1 in Cephalalgia.
The analysis included 60 patients aged 18 to 65 years with TTH (8 or more headache days a month and 3 or fewer migraine days per month) who did not have medication overuse headaches or cervicogenic headache, previous whiplash or head trauma, and no other major physical or neurologic illness. Of these, 25 had frequent episodic TTH and 35 had chronic TTH.
The study also included 30 sex- and age-matched controls with no history of significant headache and no physical or mental illnesses.
Examiners measured maximal isometric force in the neck extensor and flexor muscles with the participants seated in an upright position with their chest strapped to a vertical plate and their arms relaxed in a custom-designed steel frame that had an attachment arm and a transducer. The transducer sends a signal to a computer, which measures the force that is exerted.
For neck extension, participants sat upright with the back of the head in front of the transducer. The attachment arm was adjusted so the back of the head touched the dynamometer at the protuberantia occipitalis.
To test neck flexion, participants sat with the forehead in front of the dynamometer. The transducer attachment arm was adjusted so the head touched the dynamometer at the level of the eyebrows.
Participants were instructed to slowly build up the force to maximal strength within 2 seconds and then exert maximal pressure for about 3 seconds before slowly relaxing. They were allowed a 30-second rest between each attempt.
Using the same equipment, examiners tested isometric shoulder muscle strength while participants were in a supine position, with their arms in a 90-degree angle and 5 degrees from the frontal plate, and with elbows slightly bent. Participants were asked to press as fast and forcefully as possible while they moved their arms upward.
Study participants kept track of the frequency, intensity, and duration of headaches in a headache diary. They registered intensity on a 0 to 10 numeric rating scale (with 0 being no pain). On the test day, they registered intensity on a visual analog scale.
The researchers found a significant difference in the neck extension strength between patients with TTH and controls (17.07 vs 21.49 Nm [a measure of torque or ‘moment’]; P = .02). There was no significant difference in neck flexion moment between patients with TTH and controls.
The relatively weaker extension muscles resulted in a significantly lower extension/flexion ratio for patients with TTH compared with controls (1:1.54 vs 1.172 Nm; P = .03).
This lower ratio “indicates that a higher relative loading of the neck extensor muscles could be present in everyday activities,” write the authors. “This possibly contributes to additional tension in the extensor muscles as well as disturbed stabilization in the neck and coordination of head movements.”
A reduced extension/flexion ratio may contribute to TTH onset and eventually to the development of chronic TTH, said the authors.
There was a borderline significant difference between the two groups for shoulder abduction strength (38.7 vs 44.3 Nm; P = .05).
Twelve patients in the study had coexisting migraine (8 had 1 migraine day per month and 4 had 2 migraine days a month). TTH patients with and without migraine did not differ for any of the tests, although none of these patients were tested on days they had a migraine.
The presence of active trigger points in patients with headache could explain some of the reduced force in the neck extensor muscles, said Madsen. “We didn’t look at trigger points in our study, but it’s known that muscle pain can contribute to reduced force in general and therefore trigger points could potentially contribute to a reduced force.”
The descending part of the trapezius is one of the most common tender muscles in patients with TTH. This muscle has an important function in both neck extension and shoulder abduction. A tender trapezium could be a reason why both the extension and abduction muscles are affected in the TTH group, said Madsen.
“This could partly explain why some of these muscles get more and more tense over time and that the more often you have tension-type headaches, the more tender these muscles are.”
A painful trapezius can contribute to headache, added Madsen. The nerves of the upper neck and shoulder muscles are connected to the trigeminal nerve at the front of the head. “So when you have pain in the neck and shoulder muscles, or muscles that are innervated by the same nerves, the pain can be felt in the front of the head.”
The authors have now completed a randomized controlled trial on the effect of strength training of the trapezius muscle in the 60 patients with TTH from the current case-control study. Madsen said he hopes to have the results published in the fall.
Asked to comment, Peter Goadsby, MD, PhD, director, Headache Center, University of California, San Francisco, said the new paper reports “an interesting finding” among patients with TTH.
“The muscle hypothesis in tension-type headache has waxed and waned over the years and so it is appropriate to re-visit the question,” said Dr Goadsby.
Patients with TTH are often said to have pericranial tenderness. “One must ask whether pain restricts effort in these subjects that then manifests as weakness,” added Dr Goadsby. “There is much to be done to understand this problem better.”
The study was funded by the Tryg Foundation.