The results of this study can be used by clinicians to identify and monitor potential fallers in MS patients.

This pilot study did not show more benefits from undertaking dual-task training than single-task training. A power analysis showed 71 patients per group would be needed to determine whether there was a clinically relevant difference for dual-task gait speed between the groups.

Background: Falling is a significant problem in patients with multiple sclerosis (MS) and the majority of falls occur during dynamic activities. Recently, there have been evidences focusing on falls and local stability of walking based on dynamic system theory in the elderly as well as patients with cerebral concussion. However, in patient with MS, this relationship has not been fully investigated. The aim of this study was to investigate local stability of walking as a risk factor for falling in patients with MS. Methods: Seventy patients were assessed while walking at their preferred speed on a treadmill under single and dual task conditions. A cognitive task (backward counting) was used to assess the importance of dual tasking to fall risk. Trunk kinematics were collected using a cluster marker over the level of T 7 and a 7-camera motion capture system. To quantify local stability of walking, maximal finite-time Lyapunov exponent was calculated from a 12-dimensional state space reconstruction based on 3-dimensional trunk linear and angular velocity time series. Participants were classified as fallers (≥1) and non-fallers based on their prospective fall occurrence. Findings: 30 (43%) participants recorded ≥1 falls and were classified as fallers. The results of multiple logistic regression analysis revealed that short-term local dynamic stability in the single task condition (P < 0.05, odds ratio = 2.214 (1.037-4.726)) was the significant fall predictor. Interpretation: The results may indicate that the assessment of local stability of walking can identify patients who would benefit from gait retraining and fall prevention programs.

The inability to produce efficient APAs and CPAs during perturbations may explain the high rates of postural instability and falls in patients with MS. Findings from this study provide a background for the development of perturbation-based training programs aimed at balance improvement and fall prevention by restoring mechanisms underlying balance impairments.

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.

The findings may reflect successful adaptation of locomotor system to preserve cognitive task performance under cognitive dual-task condition. Future studies should examine more complex concurrent cognitive and motor tasks to better understand the dual-task-related gait changes and their contribution to falls in patients with MS.

III.

Impaired balance is one of the most disabling multiple sclerosis (MS) symptoms. It is known that, in the presence of predictable perturbations, the central nervous system (CNS) utilizes both anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain balance. The main purpose of this study was to investigate the relationship between APAs and CPAs during self-induced postural perturbation in patients with MS. Participants performed a load release task while standing on a force platform. Electrical activity of six leg and trunk muscles, as well as displacements of the center of pressure (COP), was recorded. The results revealed significant APAs deficits in MS patients reflected in short APAs duration and reduced magnitude. The reduced APAs were not accompanied by significant compensatory muscle activity. It can be concluded that there is an impairment of feed-forward postural control in MS, and feedback-based mechanisms (CPAs) are unable to compensate for these APA deficits. These results should be considered in the rehabilitation programs for balance training of MS patients.