Postural instability can increase the likelihood of hazardous slip and fall accidents in workplaces. The present study intended to extend understanding of the effect of abnormal neck posture on postural control during quiet standing. The effect of body fatigue on the postural control was also of primary concern. Twelve healthy undergraduate students volunteered to participate in the experiment. Standing on a force platform with the neck neutral, flexed, extended, or rotated, subjects’ center of pressures (COP) were measured under the two levels of body fatigue. For the fatigue condition, Subjects exercised in a treadmill to meet the predetermined level of body fatigue. Analyzing the position coordinates of COPs, the length of postural sway path was assessed in both medio-lateral (ML) axis and anterior-posterior (AP) axis. Results showed that, in AP direction, neck extension or rotation significantly increased the sway length as compared with neck neutral. Neck extension led to greater sway length compared to neck rotation. Neck flexion did not differ from neck neutral. The sway length in the AP direction also became significantly larger as the body fatigue accumulated after treadmill exercise. In ML direction, as compared to neutral posture, the neck extension, flexion, or rotation did not significantly affect the length of postural sway path. However, the sway length seemed to increase marginally with the neck extended during the fatigued condition. This study demonstrates that abnormal neck posture may interfere with postural control during standing. The ability to maintain postural stability decreases significantly with the neck extended or rotated. Body fatigue leads to postural instability further.

This study compared the stability of the cervical spine according to the presence of neck pain and deep neck flexor performance. Thirty subjects with neck pain, and thirty subjects without neck pain were recruited for this study. The Cranio-cervical flexion (CCF) test was applied using a pressure biofeedback unit to classify the subjects into four subgroups; no cervical pain and good deep neck flexor performance (NG group), no cervical pain and poor deep neck flexor performance (NP group), cervical pain and good deep neck flexor performance (PG group), and cervical pain and poor deep neck flexor performance (PP group). The head sway angle was measured using a three-dimensional motion analysis system. A 3-kg weight was used for external perturbation with the subject sitting in a chair in the resting and erect head positions with voluntary contraction of the deep neck flexors. A one-way analysis of variance (ANOVA) was performed with a Bonferroni post hoc test. The deep neck flexor performance differed significantly among the four groups (p<.05). The NG group had significantly greater deep neck flexor performance than NP and PP groups. The stability of the cervical spine also differed significantly among the four groups in the resting head position (p<.05). The head sway angle was significantly smaller in NG group as compared with the other groups. The PP group had the greatest head sway angle in the resting head position. However, there was no significant difference in the stability of the cervical spine among the groups in the erect head position with voluntary contraction of deep neck flexors (p=.57). The results of this study suggest that the deep neck flexor performance is important for maintaining the stability of cervical spine from external perturbation.