Sit-to-stand (STS) is an important functional task affected by low back pain (LBP). It requires fundamental coordination among all segments of the body to control important performance variables such as body's center of mass (CM) and head positions. This study was conducted to determine whether LBPs could coordinate their multiple joints to achieve the task stability to the same extent as healthy controls. About 11 non-specific chronic LBP and 12 healthy control subjects performed STS task at three postural difficulty levels: rigid surface — open eyes (RO), rigid surface — closed eyes (RC) and narrow surface — closed eyes (NC). Motion variability of seven body segments, CM and head positions were calculated across 15 trials, and uncontrolled manifold (UCM) approach was used to investigate joint coordination. This approach partitioned segment angle variations into component that stabilizes a given performance variable and leads to task performance flexibility (UCM variability: V UCM ) and that which does not stabilize the performance variable and leads to task performance error (orthogonal variability: V ORT ). The results showed that LBPs demonstrated significantly less V UCM regarding the control of horizontal CM position and greater V ORT regarding the control of horizontal head position. The current findings revealed that multijoint coordination was impaired in the LBP subjects. These altered motor coordination strategies would make their postural control system less adaptive to altered postural demands and may predispose these subjects to re-injury.

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Background: Impairment of cervical sensory input in patients with neck pain may disturb postural stability. The purpose of present study was to assess the dynamic postural stability of subjects with chronic neck pain compared to a matched control group. Methods: In this case-control study, 22 chronic non-specific neck pain and 22 healthy individuals participated. Postural stability was measured with Techno-body Prokin tilting platform. Subjects performed balance tests under two conditions: eyes open and closed. The parameters for assessment of postural stability were total stability index (TSI), anteroposterior stability index (APSI), mediolateral stability index (MLSI), and trunk deviation which demonstrated total trunk sway in medio-lateral and antero-posterior. We used a separate 2 (group) by 2 (postural difficulty) mixed-design analysis of variance (ANOVA) for analysis of postural performance. Results: There were significant differences between the chronic neck pain and matched control groups in APSI, MLSI, and TSI, p<0.001 in both eyes opened and closed conditions. The trunk deviation was greater for non-specific neck pain in comparison to healthy subjects, p<0.05 in both conditions of eyes open and closed. Conclusion: The results of this study showed that patients with chronic neck pain have poorer postural control than healthy subjects. The findings suggest that clinicians take into account the importance of dynamic postural stability assessment in patients with chronic non-specific neck pain and consider the application of intervention programs for improvement of the dynamic balance.

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Sit to stand (STS) task requires variability of all body segments to achieve the stability of the important control variables (i.e., center of mass (CM) and head positions). In this study, the possible differences in the variability patterns of various body segments were investigated between 11 chronic low back pain (LBP) and 12 control subjects during STS task through two types of variability analyses; first by calculating the variability of seven limb angles, CM and head positions across 15 trials and second by principal component analysis (PCA) of seven limb angles. Participants performed the task at 3 postural difficulty levels: rigid surface, open eyes (RO), rigid surface, close eyes (RC) and narrow surface, close eyes (NC). The results revealed that LBPs could stabilize the CM and head positions same as controls. Also there was more than 1 synergic combination of whole body segments in both LBP and healthy groups. But the number of PCs accounting for the major part of variance was reduced in the LBPs in the most unstable phase of movement (50%–80% trajectory) in the RO and RC conditions. This may indicate that LBPs have reduced flexibility in the most unstable phase of task.