Fibre types of human suboccipital muscles

Understanding the functional role of the cervical muscles is important for the effective diagnosis and treatment of cervical disorders. The suboccipital muscles are targets for treatment in whiplash and chronic headache, although their function remains unclear. There are no data on suboccipital muscle fiber type composition to facilitate an understanding of their function. Suboccipital muscles (n=95; rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis superior, obliquus capitis inferior) were dissected bilaterally from 12 cadavers (6 male; mean age 81 years). Immunohistochemistry was used to identify type I/II muscle fibers. Fibers were counted using stereology (random systematic sampling) and data analyzed (descriptive statistics, ANOVA, paired and independent t-tests) to examine differences between muscles, sex and laterality (p<0.05). Mean [SD] type I fiber proportion overall was 62.3% [10.9]; rectus capitis posterior minor had the smallest proportion of type I fibers (58.8% [9.5]), obliquus capitis inferior the largest (69.2% [10.5]). There were no significant differences overall between muscles or sides. There was a significant difference between sexes overall when data from the four muscles were pooled (p=0.027), but no difference when muscles were compared separately. Individual suboccipital muscles showed similar type I/II fiber type proportions, suggesting homogenous function for muscles in this group. Fiber type composition indicated high levels of both postural and phasic activity. Conservative management of cervical disorders involving the suboccipital muscles (e.g. exercise therapy) should consider the homogenous function of this muscle group, and include rehabilitation promoting both postural and phasic function.