The muscles of the neck generate movements and maintain stability of the head and neck. Previous studies have used simplified representations of musculoskeletal anatomy to analyze neck muscle function. However, the complex geometry and architecture of the neck muscles influence their function. The goal of this thesis was to evaluate the influence of neck musculoskeletal biomechanics on neural control. This was accomplished by developing a detailed model of the cervical musculature and examining muscle activation patterns in humans under mechanically controlled conditions.

The first study focused on development of a biomechanical model of the neck that incorporates muscle morphometric data, cervical musculoskeletal anatomy and intervertebral kinematics, to analyze the moment-generating capacities of 19 neck muscles. In the neutral posture, the muscles with the greatest potential to generate moment are sternocleidomastoid for flexion and lateral bending, semispinaiis capitis and splenius capitis for extension, and trapezius and splenius capitis for axial rotation. For some neck muscles, variations in posture caused large changes in muscle moment arms and force-generating capacities.

The second study measured three-dimensional isometric moments and neck muscle electromyographic activity in human subjects. The largest moments were generated for extension (average 52 Nm for males and 21 Nm for females). Flexion and lateral bending moments were approximately 60-70% of extension moments, and axial rotation moments were 30% of extension moments. Most muscles exhibited significant antagonist muscle activation, which must be taken into account in biomechanical models.

The third study examined the spatial activation patterns, or tuning, of neck muscles. Each muscle had a preferred activation direction. Neither the preferred direction nor the spatial focus changed with load level. Preferred direction often did not correspond to the muscle’s maximum moment arm, suggesting that mechanical advantage is not the primary factor used by the central nervous system in determining neck muscle activation.

This thesis illustrates how musculoskeletal biomechanics influence neural activation patterns. The results are relevant to control of head movement in normal subjects and may be extended to analyze neurologic or musculoskeletal dysfunction.