Pamela M. Barton, MD, Keith C. Hayes, PhD
ABSTRACT. Barton PM, Hayes KC.
Neck flexor muscle strength, efficiency, and relaxation times in normal subjects and subjects with unilateral neck pain and headache. Arch Phys Med Rehabil 1996;77:680-7.
Objective: To determine the test-retest reliability of a new method for measuring muscular strength, efficiency, and relaxation times of the neck flexor musculature of healthy adults, and to compare these neck flexor muscle properties in subjects who have unilateral neck pain and headache with those in controls.
Design: Subjects lay supine and isometrically flexed their necks against a force transducer attached to the back of a webbing and velcro helmet. Electromyograms (EMGs) were recorded from surface electrodes on the stemocleidomastoid (SCM) muscles. Two consecutive sessions of five contractions of varying levels of effort from minimal through moderate and maximal effort were analyzed.
Setting: Ambulatory referral center.
Participants: Volunteer control subjects (n = 10, 3 men and 7 women) were recruited from hospital and university personnel. Volunteer neck pain subjects (n = 10,3 men and 7 women) were recruited from a physiatric chronic pain practice and a hospital outpatient physical therapy practice.
Results: In the controls, the intraclass correlation coefficients (ICCs) for the first two maximum neck flexion contractions were: peak force ICC = .81; peak force/body weight ICC = .75; average force ICC = .75; force relaxation time ICC = .73; SCM EMG relaxation times: right ICC = .60 and left ICC = .67. Comparing sessions 1 and 2 the intraclass correlations for SCM efficiencies were right ICC = 58 and left ICC = .97. The peak force in controls (Tt = 45.3 -+ 17.6N) was reduced by 50% in the neck pain subjects (X = 22.4 ? 13.lN) (p = .004). Similarly, peak force/body weight in the neck pain subjects (X = 0.3 2 0.2N/kg) was 46% of controls (K = 0.7 2 0.2N/kg) (p = .OOl), and average force in the neck pain subjects (5t = 12.1 -+ 7.5N) was 43% of controls (X = 28.5 2 ll.ON) (p = .OOl). In two neck pain subjects, SCM EMG and force relaxation times were abnormally long in both the affected and the unaffected SCM muscles, exceeding the control values by greater than 3 standard deviations. The difference between the right SCM efficiency of the control subjects (X = 0.3 t 0.2N/pV) and the affected SCM efficiency of the neck pain subjects (X = 0.1 5 0.1 NIpV) approached the p < .05 criterion for significance (p = .055).
Conclusion: The technique was found to be highly reliable for the measurement of neck flexor peak force, peak force/body weight, average force, and force relaxation time, and moderately reliable for the quantitation of SCM EMG relaxation times and SCM efficiency. All force values were significantly lower in the neck pain population compared with the controls. In the neck pain population, force and SCM EMG relaxation times, as well as efficiencies, suggested abnormalities. Neck pain subjects showed no significant differences in SCM EMG relaxation time or SCM efficiency between affected and unaffected SCM muscles. Trauma-related neck pain and headache are increasingly prevalent and costly in terms of treatment costs, income support, and lost productivity.’ Assessment and treatment of these conditions usually proves challenging. Traditional medicine has tended to focus on diagnosis rather than on management of the morbidity caused by these “benign muscle tension headaches.” For those attempting to manage this problem, success has been hampered by a lack of adequate assessment tools coupled with a poor understanding of the cause and perpetuators of the condition. At best, clinical evaluation includes use of pain diagrams and scales, examination of posture, assessment of cervical range of motion with goniometers, manual assessment for segmental spinal motion, evaluation of muscle tenderness with palpation and algometry, and attempts to evaluate neck muscle strength.*-‘* At the present time, however, there are few normative values against which to compare a patient’s status, and little information is available on how these values are associated with the underlying complaint of pain.