Promoting longus colli muscle activation: Force direction in sitting matters.

Background: There is limited evidence to inform exercise prescription for deep neck flexor activation out of supine.

Objective: To compare activation of longus colli (LC) and sternocleidomastoid (SCM) from supine to sitting, and to compare the effect of craniocervical flexion (CCF) exercises in sitting on activation.

Methods: Twenty-four individuals without neck pain (mean age 28.8 years, 12 females) completed 7 isometric CCF exercises (1 supine CCF, 6 sitting with applied head resistance through an elastic band in straight or oblique planes from the contra- or ipsilateral sides) while muscle activation was captured using ultrasound imaging. A 2-way analysis of variance examined the effects of exercise and muscle on percent change activation using planned post-hoc comparisons and Cohen's D to establish effect sizes.

Results: Supine CCF was equivocal to sitting CCF with resistance for LC activation (p = 0.758). The LC muscle was most robustly activated by applying an ipsilateral oblique resistance force compared to a straight lateral force (p = 0.002, Cohen's d = -0.82). LC activation was higher when oblique resistance was applied from the ipsilateral than contralateral side (p = 0.002, Cohen's d = -0.84). SCM activation was higher resisting an ipsilateral lateral force compared to a contralateral force (p = 0.0006, Cohen's d = 1.06).

Conclusions: Craniocervical flexion in supine and sitting activate LC equally but in sitting, applying oblique resistance during lateral flexion with extension enhances LC activation most effectively. Care should be taken with straight laterally applied forces since this can promote unwanted SCM activation.