A preliminary repeated measures study of the effect of an imposed posture on the pose of the head and upper and lower neck of seated humans.

Background: Posture of the upper neck is considered by some to contribute to neck pain and headache. Infrared reflectors and cameras permit non-invasive three-dimensional (3D) evaluation of head and neck range of motion but have not been used to examine the relative pose (position and orientation) of the head, upper and lower neck.

Research Question: Can the relative 3D pose of the head, upper and lower neck regions of adult humans be non-invasively measured and perturbated while recording the characteristics of neck or head pain?

Methods: An optical motion capture system was used in a repeat measure descriptive analysis study. Continuous recordings of the 3D position of fiducial markers affixed to the head (Hf), skin over C2 spinous process (C2f) and vertebral prominence (VPf) of adult (2 males 1 female, 27-61-year-old) volunteers free of pain were made while seated at a desktop computer that allowed recording of the characteristics of ensuing pain. Control trials involved 20 minutes of video viewing. Test trials included occlusion of upper third of visual field during the trial's second phase. Trial allocation was random, repeat trials were > 5 days apart.

Results: Median angles between Hf, C2f and VPf in control trials changed little (median 1 degree; range 0-8 degrees). Single case study effect size measure PEM-Ta, percentage of test phase observations above chance compared to the control phase trend, ranged from 13 % to 100 % (median 100 %). Test phase trial median angles between fiducial markers primarily involved Y axis (Pitch) rotations (range C2f to Hf 5-14; VPf to Hf 12-29 degrees; effect sizes 98-100 %, except one trial, 21 %) with little change about other axes.

Significance: This study provides preliminary evidence that the relative 3D pose of the head, upper and lower neck of seated adults can be non-invasively measured and perturbated while simultaneously characterising ensuing pain.