Decreased isometric neck strength in women with chronic neck pain and the repeatability of neck strength measurements.

Objectives: To evaluate neck flexion, extension, and, especially, rotation strength in women with chronic neck pain compared with healthy controls and to evaluate the repeatability of peak isometric neck strength measurements in patients with neck pain.

Design: Cross-sectional.

Settings: Rehabilitation center and physical and rehabilitation medicine department at a Finnish hospital.

Participants: Twenty-one women with chronic neck pain and healthy controls matched for sex, age, anthropometric measures, and occupation.

Interventions: Not applicable.

Main Outcome Measures: Peak isometric strength of the cervical muscles was tested in rotation, flexion, and extension.

Results: Significantly lower flexion (29%), extension (29%), and rotation forces (23%) were produced by the chronic neck pain group compared with controls. When the repeated test results were compared pairwise against their mean, considerable variation was observed in the measures on the individual level. Intratester repeatability of the neck muscle strength measurements was good in all the 4 directions tested in the chronic neck pain group (intraclass correlation coefficient range,.74-.94). The coefficient of repeatability was 15N, both in flexion and extension, and 1.8 Nm in rotation. On the group level, improvement up to 10% due to repeated testing was observed.

Conclusions: The group with neck pain had lower neck muscle strength in all the directions tested than the control group. This factor should be considered when planning rehabilitation programs. Strength tests may be useful in monitoring training progress in clinical settings, but training programs should be planned so that the improvement in results is well above biologic variation, measurement error, and learning effect because of repeated testing.