Muscle synergies during shifts of the center of pressure by standing persons

Krishnamoorthy, Vijaya; Latash, Mark L.; Scholz, John P.; Zatsiorsky, Vladimir M.

doi:10.1007/s00221-003-1574-6

Cited by 233 publications

(183 citation statements)

References 37 publications

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“…These studies assumed that no changes in the composition of M-modes happened during the execution of such tasks. This assumption has been indirectly corroborated by the observations of similar M-modes in several studies using variations of postural tasks (Krishnamoorthy et al 2003b;Wang et al 2005Wang et al , 2006DannaDos-Santos et al 2007). …”

Section: Stability and Flexibility Of Modessupporting

confidence: 54%

Learning effects on muscle modes and multi-mode postural synergies

et al. 2007

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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.

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Section: Stability and Flexibility Of Modessupporting

confidence: 54%

Learning effects on muscle modes and multi-mode postural synergies

et al. 2007

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“…Examples include the coordination of articulators during speech (Abbs and Gracco 1984), of arms during loading and unloading (Dufosse et al 1985;Paulingnan et al 1989), of joints during pointing, reaching, standing-up, and swaying (Domkin et al 2002;Freitas et al 2006;Scholz and Schöner 1999;Wang and Stelmach 1998), of muscles during standing and stepping (Krishnamoorthy et al 2003;Wang et al 2005), and of digits during pressing, grasping, and holding an object (Gao et al 2005;Santello and Soechting 2000;Scholz and Latash 1998;Shim et al 2005). Very few studies, however, have addressed synergies at different levels of an involved control hierarchy.…”

Section: Hierarchies Of Synergies In Natural Movementsmentioning

confidence: 99%

“…During pointing tasks, the subject's attention was drawn to relative motion of the two hands; nevertheless, multi-joint synergies stabilized each hand's trajectory were seen (Domkin et al 2002(Domkin et al , 2005. Similarly, during postural tasks, multi-muscle analysis revealed the presence of synergies stabilizing shifts of the center of pressure (COP, the point of application of the resultant force acting on the body from the support surface) despite the fact that no feedback was available on the COP shifts (Krishnamoorthy et al 2003;Wang et al 2005). So, although the organization of the visual feedback could play a role in our experiments, it alone seems to be insufficient to explain the results.…”

Section: Hierarchies Of Synergies In Natural Movementsmentioning

confidence: 99%

Hierarchies of synergies: an example of two-hand, multi-finger tasks

2006

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We explored the ability of the central nervous system (CNS) to assemble synergies stabilizing the output of sets of effectors at two levels of a control hierarchy. Specifically, we asked a question: can the CNS organize both two-hand and within-a-hand force stabilizing synergies in a simple two-hand force production task that involves two fingers per hand? Intuitively, one could expect a positive answer; that is, forces produced by each hand are expected to co-vary negatively across trials to bring down the total force variability, while forces produced by each finger within-a-hand are expected to co-vary negatively to reduce the variability of that hand's contribution to the total force. The subjects were instructed to follow a trapezoidal time profile with the signal corresponding to the force produced by a set of instructed fingers in one-hand tasks with two-finger force production and in two-hand tasks with involvement of both symmetrical and asymmetrical finger pairs in the two hands. Finger force co-variation across trials was quantified and used as an index of stabilization of the force produced by all the instructed fingers, and of the force produced by finger pairs within-a-hand. No major differences were seen between the dominant and the non-dominant hand and between the twohand tasks with symmetrical and asymmetrical finger involvement. Stronger synergies were seen in the index-middle finger pair as compared to the ring-little finger pair. The main result of the study is the significantly weaker or even lacking two-finger force stabilizing synergies within-a-hand during two-hand tasks while such synergies were present in one-hand tasks. This observation points at a potential limitation in the ability of the CNS to organize synergies at two levels of a control hierarchy simultaneously. It also allows suggesting a hypothesis on two types of synergies in the human motor repertoire, well-practiced synergies that form a library serving as the foundation for all novel actions, and freshly assembled synergies.

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“…Bernstein 1967). In a series of recent studies, the framework of the uncontrolled manifold (UCM) hypothesis has been used to quantify multi-muscle synergies involved in various tasks such as preparation to a self-inflicted postural perturbation (Krishnamoorthy et al 2003b), preparation to making a step (Wang et al 2005(Wang et al , 2006, and voluntary sway (Danna-Dos-Santos et al 2007). The UCM hypothesis (Scholz and Schüner 1999;reviewed in Latash et al 2002breviewed in Latash et al , 2007 assumes that the neural controller acts in a space of elemental variables, forms in that space a sub-space (UCM) corresponding to a desired value (time profile) of an important performance variable, and then confines most of the variability to that sub-space.…”

Section: Introductionmentioning

confidence: 99%

Multi-muscle synergies in an unusual postural task: quick shear force production

2008

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We considered a hypothetical two-level hierarchy participating in the control of vertical posture. The framework of the uncontrolled manifold (UCM) hypothesis was used to explore the muscle groupings (M-modes) and multi-M-mode synergies involved in stabilization of a time profile of the shear force in the anterior-posterior direction. Standing subjects were asked to produce pulses of shear force into a target using visual feedback while trying to minimize the shift of the center of pressure (COP). Principal component analysis applied to integrated muscle activation indices identified three Mmodes. The composition of the M-modes was similar across subjects and the two directions of the shear force pulse. It differed from the composition of M-modes described in earlier studies of more natural actions associated with large COP shifts. Further, the trial-to-trial M-mode variance was partitioned into two components: one component that does not affect a particular performance variable (V UCM ), and its orthogonal component (V ORT ). We argued that there is a multi-M-mode synergy stabilizing this particular performance variable if V UCM is higher than V ORT . Overall, we found a multi-M-mode synergy stabilizing both shear force and COP coordinate. For the shear force, this synergy was strong for the backward force pulses and non significant for the forward pulses. An opposite result was found for the COP coordinate: the synergy was stronger for the forward force pulses. The study shows that M-mode composition can change in a task-specific way and that two different performance variables can be stabilized using the same set of elemental variables (Mmodes). The different dependences of the ΔV indices for the shear force and COP coordinate on the force pulse direction supports applicability of the principle of superposition (separate controllers for different performance variables) to the control of different mechanical variables in postural tasks. The M-mode composition allows a natural mechanical interpretation.

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Muscle synergies during shifts of the center of pressure by standing persons

Cited by 233 publications

References 37 publications

Learning effects on muscle modes and multi-mode postural synergies

Learning effects on muscle modes and multi-mode postural synergies

Hierarchies of synergies: an example of two-hand, multi-finger tasks

Multi-muscle synergies in an unusual postural task: quick shear force production

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