Biomechanical Implications of Gender-Dependent Muscle Locations

Military pilots are subjected to high magnitude inertial loads applied to the head-neck complex during high-G maneuvers. Cervical spinal soft-tissue injuries have occurred in this population [1–3]. Acute injury rates were reported between 54 and 89%, most commonly resulting in muscle or neck pain. Early cervical spine degenerative changes were also identified for fighter pilots [4]. Because the neck muscles are responsible for maintaining head-neck stability, one study hypothesized that cervical injuries in aviators may result from insufficient neck muscle strength to support the head-neck complex during high-G maneuvers [5]. This hypothesis is supported by the finding that pilots participating in pre-injury neck strengthening exercises demonstrated fewer injuries [1]. Although clinical data on the subject are limited, female pilots may be more susceptible to neck injury due to more slender necks and cervical columns that may be less resistant to bending [6, 7]. Differences in neck muscle geometry, in terms of cross-sectional area and positioning, may also lead to differing injury rates. Previous investigations of neck muscle geometry using contemporary medical imaging modalities were conducted with subjects in supine position [8–11], which removes the axial loads of the head and superior cervical structures due to gravity and likely changes neck muscle geometry. To date, no study has outlined gender-dependent neck muscle geometry determined using MRI of subjects in upright, sitting posture. The present hypothesis was that significant gender differences exist in neck muscle geometry.