According to the Uncontrolled Manifold (UCM) approach, motor synergies allow motor flexibility while ensuring stable task performance. The stronger the motor synergies, the greater performance stabilization. Thus, just before the start of a new motor task, the synergies need to be attenuated to facilitate the initiation or change of movement. This reduction in synergy during the preparation for movement initiation is called Anticipatory Synergy Adjustments (ASAs). In individuals with neurological deficits, changes in the timing or magnitude of ASAs can result in reduced movement agility or greater difficulty initiating a new task. Additionally, altered ASAs can serve as preclinical markers of neurological dysfunctions such as Parkinson's disease or multiple sclerosis.

The aim of this study was to characterize the behavior of ASAs in populations with neurological dysfunctions and analyze their clinical implications.

A narrative review of studies that used the UCM approach to quantify ASAs in individuals with neurological dysfunctions was conducted.

The review resulted in the inclusion of 9 exploratory studies. The study samples consisted of individuals with Parkinson's disease (PD), olivopontocerebellar atrophy (OA), stroke, multiple sclerosis (MS), and cerebral palsy (CP). The motor tasks analyzed in the studies were divided into manual tasks and standing postural control tasks. In individuals with PD, MS, and OA, delayed and smaller magnitude of ASAs were observed when compared to healthy individuals. In individuals with CP and stroke, ASAs in manual tasks differed from healthy individuals in small magnitudes.

In general, the observed changes in ASAs in the study lead to reduced agility during task execution and greater difficulty initiating new movements.

The use of the UCM method and the analysis of ASAs appears to be sensitive for the early detection of some neurological conditions and tracking disease progression and intervention effects, especially in individuals with subcortical disorders. However, using UCM to evaluate patients in the clinical context is still challenging. Its application requires specific technology and knowledge, which limits its use to the search environment. It would be interesting if future studies investigated the relationship between the behavior of ASAs and performance in commonly used functional instruments/questionnaires in clinical practice so that the understanding and application of the UCM method in the clinical context can be optimized.