Coordination of muscles to control the footpath during over-ground walking in neurologically intact individuals and stroke survivors

Abstract

The central nervous system (CNS) is believed to use the abundant degrees of freedom of muscles and joints to stabilize a particular task variable important for task success, such as footpath during walking. Stroke survivors often demonstrate impaired balance and high incidences of falls due to increased footpath variability during walking. In the current study, we use the uncontrolled manifold (UCM) approach to investigate the role of motor abundance in stabilizing footpath during swing phase in healthy individuals and stroke survivors. Twelve stroke survivors and their age- and gender-matched controls walked over-ground at self-selected speed, while electromyographic and kinematic data were collected. UCM analysis partitioned the variance of muscle groups (modes) across gait cycles into “good variance” (i.e., muscle mode variance leading to a consistent or stable footpath) or “bad variance” (i.e., muscle mode variance resulting in an inconsistent footpath). Both groups had a significantly greater “good” than “bad” variance, suggesting that footpath is an important task variable stabilized by the CNS during walking. The relative variance difference that reflects normalized difference between “good” and “bad” variance was not significantly different between groups. However, significant differences in muscle mode structure and muscle mode activation timing were observed between the two groups. Our results suggest that though the mode structure and activation timing are altered, stroke survivors may retain their ability to explore the redundancy within the neuromotor system and utilize it to stabilize the footpath.

Coordination in adults with neurological impairment – A systematic review of uncontrolled manifold studies

“…No mention of strategies for avoiding fatigue was made in two studies [38,41]. The performance variables and elemental variables were clearly identified in all studies, but two studies did not justify the choice of elemental variables [24,40].…”

“…One study was found for each of the following pathologies: multiple sclerosis [44], olivo-ponto-cerebellar atrophy [45] and spinocerebellar degeneration [46]. With regard motor tasks, seven studies investigated multi-finger pressing tasks [24,32,39,41,[43][44][45], four reaching [34][35][36][37], three posture stabilization in quiet standing [25,33,43], one load release while standing [46], one pressing and prehension [42], one wrist and fingers extension [40], and one walking [38]. The most commonly used performance variables were the trajectory of center of pressure in balance tasks [25,33,43,46], total pressing force in finger pressing tasks [32,39,41,44,45] and hand position in reaching tasks [34,35,37].…”

“…The most commonly used performance variables were the trajectory of center of pressure in balance tasks [25,33,43,46], total pressing force in finger pressing tasks [32,39,41,44,45] and hand position in reaching tasks [34,35,37]. For these tasks, the most commonly used elemental variables were multi-muscle modes [25,33,36,38,43,46,47], multi-finger modes [32,39,41,42,44,45] and joint angles [34,35,37].…”

“…See Table 1b for details of the UCM checklist. All studies described the task used for UCM analysis in detail, except for Srivastava et al (2016) [38]. This study investigated synergies stabilizing foot trajectory during the swing phase in overground walking.…”

“…Eight studies consistently found reduced SI (weaker synergies) for patients with Parkinson's disease [24,25,[41][42][43] olivo-ponto-cerebellar atrophy [45], multiple sclerosis [44], compared to healthy controls. Five studies did not report the specific changes in VUCM or VORT that led to SI reduction [25,38,41,43,45]. Two studies found VUCM was reduced (less flexibility) in patients with multiple sclerosis [44] and Parkinson's disease [42], one study found unchanged VUCM in Parkinson's disease [24], and one found increased VUCM (more flexibility) in spinocerebellar degeneration [46].…”