The Role of Anticipatory Postural Adjustments and Compensatory Control of Posture in Balance Control of Patients With Multiple Sclerosis

Abstract

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.

Effects of External Perturbations on Anticipatory and Compensatory Postural Adjustments in Patients with Multiple Sclerosis and a Fall History

“…The inability to produce efficient APAs during expected perturbations and CPAs during unexpected perturbations as the first line of defense against perturbations may explain the high rates of postural instability and falls in these patients. 10,29 By inducing both predictable and unpredictable external perturbations in the present experiment, we were able to observe a sequence of events in the muscular activity, from APAs to CPAs. It has been shown that when the perturbation is predictable, APAs act as the first line of defense, preparing the body for the upcoming disturbance, followed by CPAs if the perturbation is large enough or poorly predicted.…”

“…8,9 Small and/or predicted perturbations can only be counteracted with APAs. 10 However, when perturbations are large and/or unexpected, CPAs are the main mechanism of balance restoration. 10,11 These two types of postural adjustments interact to maintain equilibrium, and the availability of APAs determines the amount of compensatory muscle activity.…”

“…10 However, when perturbations are large and/or unexpected, CPAs are the main mechanism of balance restoration. 10,11 These two types of postural adjustments interact to maintain equilibrium, and the availability of APAs determines the amount of compensatory muscle activity. 10 Recent studies have shown that inefficient postural adjustment mechanisms in older adults can lead to accidental falls.…”

“…10,11 These two types of postural adjustments interact to maintain equilibrium, and the availability of APAs determines the amount of compensatory muscle activity. 10 Recent studies have shown that inefficient postural adjustment mechanisms in older adults can lead to accidental falls. [12][13][14] Elderly individuals with a fall history demonstrated slow and inefficient APAs during the precrossing phase of obstacle walking.…”

“…Studies of postural adjustments in patients with MS have shown decreased magnitude and increased latency of muscle activations in APAs during voluntary load release tasks 10,11 and also in response to external perturbations (ie, pendulum impact). 16 Although these studies provide important information on the strategies of postural adjustments in patients with MS, it is still unknown whether there are differences in the impairments of underlying mechanisms of postural control ing of an upcoming perturbation and 2) unexpected perturbations were those applied without verbal warning of an impending perturbation.…”