RELIABILITY OF CERVICAL EXTENSION AND ROTATION ISOMETRIC STRENGTH TESTING IN SYMPTOMATIC SUBJECTS
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Objectives The purposes of this study were: 1) To assess the reliability of cervical extension and rotation isometric strength testing of subjects who were experiencing neck pain at the time of testing, and 2) To determine if there is an association between cervical strength and neck pain intensity, or level of neck disability, or fear of neck movement, or cervical range of motion. Design A reliability study of repeated measurements of isometric cervical extension and rotation strength and a correlational study to assess the association between strength and pain, disability, fear of movement, and range of motion of the cervical spine were conducted on a sample of symptomatic subjects. Participants Two groups (N = 60 & N = 55) of volunteers with neck pain were recruited by advertisements located in a private chiropractic clinic and a hospital bulletin board. The group for cervical extension strength testing consisted of 25 men (age = 38 ± 14 yr; disability = 28 ± 16%; pain = 29 ± 25mm) and 35 women (age = 36 ± 12 yr; disability = 26 ± 15%; pain = 31 ± 26 mm). The other group for cervical rotation strength testing consisted of 25 men (age = 40 ± 11 yr; disability = 25 ± 13%; pain = 22 ± 20mm) and 30 women (age = 37 ± 11 yr; disability = 29 ± 13%; pain = 31 ± 24mm). Main Outcome Measures: Cervical extension strength was measured on an isometric extension strength testing machine (MedXTM Cervical Extension Machine). Cervical rotation strength was measured on an isometric rotation strength testing machine (MedXTM Cervical Rotation Machine). Strength testing was carried out in 2 testing sessions (48 hours apart). Prior to each testing session all participants completed a visual analogue scale for neck pain and a neck disability questionnaire. In addition, individuals who took part in cervical rotation strength testing completed a visual analogue scale for fear of neck movement and had their cervical range of motion measured. Results Cervical extension strength testing (ICC = 0.949, 95% CI = 0.9477 - 0.9502) and cervical rotation strength testing (ICC = 0.965, 95% Cl = 0.9645 - 0.9663) were reliable. Standard error of measurement (SEM) values for cervical extension strength and cervical rotation strength were 23% and 6%, respectively. A multiple regression analysis did not reveal any significant association between cervical strength and neck pain intensity, or level of neck disability, or fear of neck movement, or cervical range of motion. Conclusion The reliability of both cervical extension and rotation strength measurements in subjects who are experiencing neck pain at the time of testing was good with a clinically acceptable level of precision. There was no association between cervical strength, neck pain intensity, fear of neck movement or cervical range of motion but the sample size for a multiple regression analysis was too small.