Influence of imposed head movements on head kinematics

Background and aim: Having adequate head support is of great importance for individuals in wheelchairs that have problems with head stabilization. Currently, the majority of head support systems are static devices that fixate the head in one position. This has limitations, because activities of daily living (such as reading or eating) and posture changes might require different head positions. We therefore have the goal to develop an intelligent head support system in which the user can intuitively control the head position while head stabilization is ensured. As a first step in this development, we aimed to study head kinematics in free space and investigate how individuals respond to imposed head movements.  Methods: Non-impaired individuals participated in this study. Participants moved their head in free space and were also placed in a measurement device (see Figure 1) which allowed us to move the head. Markers were placed on the head, torso and the head support system to study the movements of these segments using an opto-electronic motion analysis system. Participants performed flexion/extension, lateroration, lateroflexion and the combination of laterorotation and lateroflexion (latter one only in the measurement device).  Results: A total of 19 participants were included in this study. We analyzed the first 10 individuals for this abstract. With respect to moving in free space, the results showed the following. Flexion and extension is an isolated movement in which only minimal lateroflexion or laterorotation take place (<5°). During laterorotation extension and contralateral lateroflexion occur towards the movement extremes (10-15°). For lateroflexion, we saw variable results in which in some individuals lateroflexion was paired with flexion and laterorotation and in other no noticeable other movements were made. With respect to the imposed movements, the results showed the following. For flexion and extension, moving the head support over a fixed point of rotation does not correspond with the movement of the head. At movement extremes, the head lost contact with the head support. Isolated laterorotation of the head support did not correspond well with the head movement, because lateroflexion of the head occurred also during this movement. For lateroflexion, moving the head support over a fixed point of rotation, the head lost contact with the head support at movement extremes. The combination of laterorotation and lateroflexion resulted in good match between the movements of the head support and the head itself with minimal movements over the flexion/extension axis (<5°).  Conclusions: When moving the head with the use of a head support system, different axes should allow a certain degree of freedom to allow natural head movements. Furthermore, flexion and extension and lateroflexion should not be controlled over a fixed point of rotation. These results can quantify optimal movement paths to be implemented in the head support system.