Meeting Abstract
The locomotor function of the neck muscles of humans is not understood. We hypothesized three possible roles: 1) stabilization of the head on the trunk; 2) stabilization of the neck against moments imposed by extrinsic arm muscles, and 3) stabilization of the trunk against torques imposed by extrinsic leg muscles. To examine these hypotheses, we measured activity of several cervical muscles with surface EMG and analyzed changes in activity in response to manipulations of the locomotor forces as subjects ran on a treadmill. To access the postural role of the cervical muscles during running we increased the mass of head by 20%. To address the impact of moments imposed on the neck by swinging of the arms, subjects held their arms at their sides as they ran. To determine the extent by which cervical muscles help stabilize the trunk against moments imposed on the pelvis, we applied forward-, rearward-, and vertically-directed forces to the subject’s pelvis with elastic tethers. Muscle activity recorded during manipulation trials was compared to activity recorded during unencumbered running at the same speed. We found no significant change in muscle activity when subjects ran with added head mass or with limited arm swing. Activity increased in the cervical strap muscles when subjects ran with increased forward-directed forces (requiring elevated leg protraction moments) and increased rearward-directed forces (requiring elevated leg retraction moments). Running with added rearward force also resulted in elevated activity of the semispinalis, levator scapulae, and rectus abdominis. These results are consistent with the suggestion that the primary function of the cervical muscles during human running is to help stabilize the trunk against the moments imposed on the pelvis by extrinsic muscles of the legs.
