Craniocervical orientation affects muscle activation when exercising the cervical extensors in healthy subjects

Objective To evaluate the activity of neck extensor muscles during different extension exercises with muscle functional magnetic resonance imaging (mfMRI). Design Cross-sectional. Setting University laboratory. Participants Healthy subjects (N=11; 7 men, mean age ± SD, 34±5.6y; 4 women, mean age ± SD, 23.3±5.2y; group mean age ± SD, 30.1±7.5y). Intervention Not applicable. Main Outcome Measures mfMRI measures of T2 relaxation were made for the multifidus (Mul), the semispinalis cervicis (SCe), the semispinalis capitis (SCa), and the splenius capitis (SpC) at C2-3, C5-6, and C7-T1 in response to 2 head/neck orientations: craniocervical neutral (CCN) and craniocervical extension (CCE). Subjects performed three 1-minute repetitions of each condition at 20% maximum voluntary contraction. Results Significant shifts were observed in all muscle groups at the C5-6 and C7-T1 levels after both conditions (P=.04) except the SpC muscle at C5-6 with CCN (P=.17). T2 shifts in the SCa were significantly greater in response to CCE than CCN at C2-3 (P=.03) and C5-6 (P=.02). Similarly, CCE resulted in larger shifts than CCN in the Mul/SCe at C7-T1 (P=.003). No segmental differences were observed between exercises for SpC (P=.25). Conclusions The results of this study provide some preliminary insight into the impact of craniocervical orientation on the differential response of the deep and superficial cervical extensor muscles during the performance of cervical extensor exercises.