Head stabilization strategies in the sagittal plane during locomotor tasks

Head stability is the dynamic process of maintaining an equilibrium position of the head-in-space. Individuals with vestibular deficits restrict head movements during dynamic activities in an effort to adapt to vestibular loss. However, this strategy does not provide them with a successful means for adaptation during dynamic tasks where head movements are required. Therefore, identification of successful head stabilization strategies is the first step towards improving the rehabilitation of these patients. The purpose of the present study was twofold: to characterize the sagittal plane head stabilization response during walking; and to identify successful head stabilization strategies during normal walking and during a walking task that challenged head stability.

The study used a repeated-measures design. Eight healthy volunteers walked normally (normal condition) and walked whilst swinging their arms at twice the natural frequency (frequency condition). Head and trunk angular velocities were measured to determine head velocity magnitudes, and head-on-trunk, with respect to trunk gains and phases across the frequency spectrum of walking.

The frequency condition increased the challenge to head stabilization and produced phases indicative of increased head stability (p < 0.05). Post hoc analyses revealed that the shift in phase occurred at higher frequencies (> 8 Hz) (p < 0.05). Increased head velocity magnitudes (p < 0.05) accompanied by decreased variability (p < 0.05) were also found at higher frequencies for the frequency condition.

The results were indicative of a tightly controlled movement strategy that ensured head stabilization under conditions where head stability was challenged. This strategy was characterized by head-on-trunk movement that was equal and opposite to trunk motion.