Background and Purpose; A common characteristic of individuals with neck pain is weakness of the anterior and posterior neck musculature. While it is difficult to compare absolute strength values secondary to differences in individuals, strength ratios are frequently used to make these comparisons. A consistent ratio for the cervical extensors and flexors has not been established among current research. The purpose of this study was to 1) compare mean differences between isometric neck flexion and extensor strength in neutral using normal subjects, and 2) determine the extensor-flexor ratio for the neck musculature.
Methods. Cervical isometric extension-flexion strength ratios were assessed in 48 subjects, 32 of which were females and across three age groups. Measurements were collected using an Interface™ strain-gauge dynamometer. A reliability study was completed to determine intra-day reliability.
Results. The reliability study found Pearson's Correlation Coefficients at r=.90 for flexion. and r=.89 for extension. A two-tailed t-test found no significant differences (p < .05) between trials. The main study found average extensor-flexor ratios for males 20-29 at 1.09:1, 30-39 at 1.04: 1, and 40-49 at 1.01: 1. The average extensor-flexor ratios for females 20-29 were found to be 1.33:1, 1.67:1 for subjects 30-39, and 1.42:1 for subjects 40-49. No significant differences were found for flexor values among male or female age groups, or in extensor-flexor ratios across all male age groups. Significant findings include: average male peak extension forces in the 40-49 age group were higher as compared to the 30-39 age group; the male 20-29 age group also had higher average peak extension forces compared to the 30-39 age group; female peak extension forces for the 30-39 age group is higher than those of the 40-49 age group~ female extensor-flexor ratios for the 30-39 age group were higher than the 20-29 age group; male extension and flexion forces were higher than females for the 20-29 and 40-49 age groups; and finally male extensor-flexor ratios were lower than females for the 20-29 and 30-39 age groups.
Discussion and Conclusion. Maximal isometric cervical strength and extensor-flexor ratios vary with changes in neck position, which may account for some of the discrepancy among reported values. In the neutral position with strain-gauge dynamometry, males' cervical strength averages reveal a 1.07: 1.0 extensor-flexor ratio while females approximate a 1.47:1.0 ratio. Peak strength occurred in the 40-49 age group for males and 30-39, age group for females. There does not appear to be a linear relationship between strength and age for individuals between 20 and 49 years old. In addition, our study suggests that strain-gauge dynamometry is a reliable technique used to measure cervical strength.
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