Undershooting of a neutral reference position by asymptomatic subjects after cervical motion in the sagittal plane

The objective of this study was to determine if blindfolded, asymptomatic subjects undershoot or overshoot a self-selected neutral reference position (NRP) when performing a full-cycle, head repositioning accuracy test in the sagittal plane.

An asymptomatic group of subjects, consisting of 7 men and 5 women with no history of head and neck pain, were recruited for the study. Subjects, performing a full-cycle series of head/neck movements in the sagittal plane, attempted to return to a self-selected NRP, defined at the beginning of the movement sequence, without benefit of visual clues. Data were collected for each subject, and repositioning errors were calculated. The sign of the error was used to determine if undershooting or overshooting of the NRP had occurred.

Subjects undershot a self-selected NRP at statistically significant levels (P < .01) when performing the head repositioning accuracy test while blindfolded. Subjects undershot the NRP 83% of the time when moving from flexion to the NRP and undershot the NRP 92% of the time when moving from extension to the NRP. A Fisher exact test showed no significant difference between the number of times subjects undershot the NRP when moving from either flexion to the NRP or from extension to the NRP. To our knowledge, neither undershooting nor overshooting of an NRP has previously been reported for asymptomatic subjects at statistically significant levels.

Knowing that asymptomatic subjects undershoot an NRP may help to direct treatment and rehabilitation of patients who have experienced whiplash-type injuries and are shown to overshoot the NRP when performing the same test.