Orientation of the Head and Trunk During Functional Upper Limb Movement

Upper limb activities imply positioning of the head with respect to the visual target and may impact trunk posture. However, the postural constraints imposed on the neck remains unclear. We used kinematic analysis to compare head and trunk orientation during arm movements (pointing) with isolated movements of the head (heading). Ten right-handed healthy adults completed both experimental tasks. In the heading task, subjects directed their face toward eight visual targets placed over a wide frontal workspace. In the pointing task, subjects pointed to the same targets (each with their right arm). Movements were recorded using an electromagnetic spatial tracking system. Both orientation of the head and trunk in space (Euler angles) and orientation of the head relative to the trunk were extracted. The orientation of the head in space was closely related to target direction during both tasks. The trunk was relatively stable during heading but contributed to pointing, with leftward axial rotation. These findings illustrate that the neck compensates for trunk rotation during pointing, engaging in specific target-dependent 3D movement in order to preserve head orientation in space. Future studies may investigate neck kinematics of people experiencing neck pain in order to identify and correct inefficient movement patterns, particularly in athletes.