We used the framework of the uncontrolled manifold hypothesis to explore the effects of practice on the composition of muscle groups (M-modes) and multi-M-mode synergies stabilizing the location of the center of pressure (COP). In particular, we tested a hypothesis that practice could lead to a transition from co-contraction muscle activation patterns to reciprocal patterns. We also tested a hypothesis that new sets of M-modes would form stronger synergies stabilizing COP location. Subjects practiced load release tasks for five days while standing on a board with a narrow support surface ("unstable board"). Their M-modes and indices of multi-M-mode synergies were computed during standing without instability and during standing on an unstable board before practice, in the middle of practice, and at the end of practice. During standing without instability, subjects showed two consistent M-modes uniting dorsal and ventral muscles of the body respectively (reciprocal modes). While standing on an unstable board, prior to practice, subjects commonly showed M-modes uniting muscle pairs with opposing actions at major leg joints -co-contraction modes. Such sets of M-modes failed to stabilize the COP location in the anterior-posterior direction. Practice led to better task performance reflected in fewer incidences of lost balance. This was accompanied by a drop in the occurrence of co-contraction M-modes and the emergence of multi-mode synergies stabilizing the COP location. We conclude that the central nervous system uses flexible sets of elemental variables (modes) to ensure stable trajectories of important performance variables (such as COP location). Practice can lead to adjustments in both the composition of M-modes and M-mode covariation patterns resulting in stronger synergies stabilizing COP location.
We investigated co-varied changes in muscle activity during voluntary sway tasks that required a quick shift of the center of pressure (COP). We hypothesized that multi-muscle synergies (defined as task-specific covariation of elemental variables, muscle modes) stabilize a COP location in the anterior-posterior direction prior to a voluntary COP shift and that during the shift the synergies would weaken. Standing subjects performed two tasks, a cyclic COP shift over a range corresponding to 80% of the maximal amplitude of voluntary COP shift at 1 Hz and a unidirectional quick COP shift over the same nominal amplitude. The cyclic sway task was used to define muscle modes (M-modes, leg and trunk muscle groups with parallel scaling of muscle activation level within a group) and the relations between small changes in the magnitudes of M-modes [in the principal component analysis (PCA), the M-mode magnitudes are equivalent to PC scores] and COP shifts. A novel approach was used involving PCA applied to indices of muscle integrated activity measured both within a trial and across trials. The unidirectional sway task was performed in a self-paced (SP) manner and under a typical simple reaction time (RT) instruction. M-modes were also defined along trials at those tasks; they have been shown to be similar across tasks. Integrated indices of muscle activity in the SP-sway and RT-sway tasks were transformed into the M-modes. Variance in the M-mode space was partitioned into two components, one that did not affect the average value of COP shift (V (UCM)) and the other that did (V (ORT)). An index (DeltaV) corresponding to the normalized difference between V (UCM) and V (ORT) was computed. During steady-state posture, DeltaV was positive corresponding to most M-mode variance lying in a sub-space corresponding to a stable COP location across trials. Positive DeltaV values have been interpreted as reflecting a multi-M-mode synergy stabilizing the COP location. The magnitude of DeltaV was larger in SP trials than in RT trials. During voluntary COP shifts, the DeltaV magnitude dropped to zero or even became negative. We conclude that M-mode synergies stabilize COP location during quiet standing, while these synergies weaken or disappear during fast voluntary COP shifts. Under RT conditions, the COP stabilizing synergies were weaker supposedly to facilitate a quick COP shift without time for preparation. The suggested method of M-mode identification may potentially be applied to analysis of postural synergies in persons with impaired postural control such as elderly persons, persons with atypical development, or in the course of rehabilitation after an injury.
The purpose of this study was to investigate postural muscle synergies (M-modes) and quantitative multi-mode coordination to ensure reproducible center of pressure (COP) in anterior-posterior trajectories associated with voluntary-induced perturbations in patients with mild cerebellar ataxia. We applied the framework of the uncontrolled manifold hypothesis for the patients with ataxia. Nine patients diagnosed with spinocerebellar degeneration (SCD) and nine healthy adults stood on a force plate performed the voluntary unloading task. Ground reaction forces and surface electromyogram signals of ten trunk and leg muscles were recorded. Total variance of the first three principal components in the SCD group was similar to the control group. The co-contraction M-modes, uniting muscle pairs with opposing actions at major leg joints, were observed more frequently in the SCD group than in the control group during anticipatory postural adjustments. The quantitative multi-mode coordinations to ensure stable COP trajectories prior to and after motor actions were smaller in the SCD group than in the control group. We conclude that individuals with mild cerebellar ataxia organize feedforward muscle modes and show more co-contraction modes and impaired coordination during feedback and feedforward postural control.
ObjectivePrevious studies have reported that elderly victims of natural disasters might be prone to a subsequent decline in motor function. Victims of the Great East Japan Earthquake (GEJE) relocated to a wide range of different types of housing. As the evacuee lifestyle varies according to the type of housing available to them, their degree of motor function loss might also vary accordingly. However, the association between postdisaster housing type and loss of motor function has never been investigated. The present study was conducted to investigate the association between housing type after the GEJE and loss of motor function in elderly victims.MethodsWe conducted a prospective observational study of 478 Japanese individuals aged ≥65 years living in Miyagi Prefecture, one of the areas most significantly affected by the GEJE. Information on housing type after the GEJE, motor function as assessed by the Kihon checklist and other lifestyle factors was collected by interview and questionnaire in 2012. Information on motor function was then collected 1 year later. The multiple logistic regression model was used to estimate the multivariate adjusted ORs of motor function loss.ResultsWe classified 53 (11.1%) of the respondents as having loss of motor function. The multivariate adjusted OR (with 95% CI) for loss of motor function among participants who were living in privately rented temporary housing/rental housing was 2.62 (1.10 to 6.24) compared to those who had remained in the same housing as that before the GEJE, and this increase was statistically significant.ConclusionsThe proportion of individuals with loss of motor function was higher among persons who had relocated to privately rented temporary housing/rental housing after the GEJE. This result may reflect the influence of a move to a living environment where few acquaintances are located (lack of social capital).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.