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.
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The authors would like to thank the Delaware Rehabilitation Institute (DRI) research core in helping with recruitment, scheduling, and clinical evaluations of the subjects.
This work was supported by Grant R01HD038582 from the National Institutes of Health (NIH).
Conflict of interest
We have no conflicts of interest to disclose.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants included in the study.
John P. Scholz: Deceased.
A correction to this article is available online at https://doi.org/10.1007/s00221-018-5240-4.
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Srivastava, S., Kao, PC., Reisman, D.S. et al. Coordination of muscles to control the footpath during over-ground walking in neurologically intact individuals and stroke survivors. Exp Brain Res 234, 1903–1914 (2016). https://doi.org/10.1007/s00221-016-4593-9
- Footpath variability
- Uncontrolled manifold hypothesis