Postural response characterization of standing humans to multi-directional, predictable and unpredictable perturbations to the arm

Forghani, Ali; Preuss, Richard; Milner, Theodore E.

doi:10.1016/j.jelekin.2016.12.003

Cited by 7 publications

(13 citation statements)

References 28 publications

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“…Statistical analyses were performed in order to investigate the effect of direction and stance width on mrEMG amplitude for the muscles of the perturbed arm and the ankles. As shown in Table 2, there was no interaction effect but there was a main effect of direction for most muscles consistent with our previous results (Forghani et al, 2017) that the pattern of changes in mrEMG was unique for each perturbation direction. There was no main effect of stance width for any muscle, but there were significant interaction effects for MRr and MGl.…”

Section: Emg Activity In Relation To Kinetic and Kinematic Responsessupporting

confidence: 90%

“…2, there was no change in ankle rotation about any axis until 115-190 ms following perturbation onset for all stance widths. We have previously shown that the body segment displacement induced by unpredictable perturbations to the arm was generally characterized by a hand-to-legs progression of movement (Forghani et al, 2017). Here, we have further shown this trend does not depend on stance width.…”

Section: Kinematic Postural Responsesupporting

confidence: 71%

“…In addition, we showed that the pattern of muscle activation is tuned to the direction of the 14 ± 3 38 ± 6 42 ± 6 20 ± 3 26 ± 4 DA 44 ± 5 44 ± 5 0 0 31 ± 6 26 ± 5 70 ± 6 73 ± 5 DP 9 ± 2 8 ± 2 15 ± 3 13 ± 3 64 ± 4 68 ± 4 16 ± 5 18 ± 4 MGr 88 ± 5 49 ± 6 48 ± 5 57 ± 5 0 3 ± 0 0 0 MGl 0 1 2 ± 3 6 8 ± 4 6 9 ± 4 7 0 ± 5 2 7 ± 3 0 0 TAr 41 ± 7 11 ± 2 7 ± 2 7 ± 2 21 ± 6 4 ± 1 71 ± 6 77 ± 6 TAl 3 2 ± 4 2 ± 0 8 ± 2 6 ± 1 2 6 ± 7 1 2 ± 3 6 1 ± 6 6 7 ± 5 PLr 45 ± 5 42 ± 5 52 ± 6 58 ± 4 14 ± 2 25 ± 5 32 ± 7 36 ± 8 PLl 12 ± 2 12 ± 2 57 ± 6 55 ± 4 41 ± 5 35 ± 4 24 ± 6 23 ± 6 (Forghani et al, 2017). Now we show that the response is not immutable but depends on the position of the feet.…”

Section: Discussionmentioning

confidence: 96%

“…This suggests that the central nervous system may be able to rapidly extract information from the hands about the direction of a disturbance, even when the disturbance is not anticipated, and activate lower limb muscles to counteract the destabilizing effect of the disturbance to balance. We have recently shown that lower limb muscles respond to handle perturbations with direction specific tuning at relatively short latencies (50-100 ms) before there are any detectable changes in the upright posture and the center of pressure (COP) (Forghani et al, 2017). However, in that study we did not test whether these responses are invariant or can be modulated according to changing demands on stability.…”

Section: Introductionmentioning

confidence: 89%

“…The maximum isometric force amplitude in the weakest direction (usually 0°) was taken as the MEF of the subject. The subjects' mean MEF was 121.5 ± 29.9 N (Forghani et al, 2017). The peak force of each perturbation during testing was set to 10%, 20% or 30% of MEF and applied in a pseudo-randomized order.…”

Section: Methodsmentioning

confidence: 99%

See 4 more Smart Citations

Short-latency muscle response patterns to multi-directional, unpredictable perturbations to balance applied to the arm are context dependent

2017

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Section: Emg Activity In Relation To Kinetic and Kinematic Responsessupporting

confidence: 90%

Section: Kinematic Postural Responsesupporting

confidence: 71%

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 89%

Section: Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Short-latency muscle response patterns to multi-directional, unpredictable perturbations to balance applied to the arm are context dependent

2017

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Stability of vertical posture explored with unexpected mechanical perturbations: synergy indices and motor equivalence

2018

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We explored the relations between indices of mechanical stability of vertical posture and synergy indices under unexpected perturbations. The main hypotheses predicted higher posture-stabilizing synergy indices and higher mechanical indices of center of pressure stability during perturbations perceived by subjects as less challenging. Healthy subjects stood on a force platform and held in fully extended arms a bar attached to two loads acting downward and upward. One of the loads was unexpectedly released by the experimenter causing a postural perturbations. In different series, subjects either knew or did not know which of the two loads would be released. Forward perturbations were perceived as more challenging and accompanied by co-activation patterns among the main agonist-antagonist pairs. Backward perturbation led to reciprocal muscle activation patterns and was accompanied by indices of mechanical stability and of posture-stabilizing synergy which indicated higher stability. Changes in synergy indices were observed as early as 50-100 ms following the perturbation reflecting involuntary mechanisms. In contrast, predictability of perturbation direction had weak or no effect on mechanical and synergy indices of stability. These observations are interpreted within a hierarchical scheme of synergic control of motor tasks and a hypothesis on the control of movements with shifts of referent coordinates. The findings show direct correspondence between stability indices based on mechanics and on the analysis of multi-muscle synergies. They suggest that involuntary posture-stabilizing mechanisms show synergic organization. They also show that predictability of perturbation direction has strong effects on anticipatory postural adjustment but not corrective adjustments. We offer an interpretation of co-activation patterns that questions their contribution to postural stability.

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Muscle synergies for multidirectional isometric force generation during maintenance of upright standing posture

Monte,

Benamati,

Pavan

et al. 2024

Exp Brain Res

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Muscle synergies are defined as coordinated recruitment of groups of muscles with specific activation balances and time profiles aimed at generating task-specific motor commands. While muscle synergies in postural control have been investigated primarily in reactive balance conditions, the neuromechanical contribution of muscle synergies during voluntary control of upright standing is still unclear. In this study, muscle synergies were investigated during the generation of isometric force at the trunk during the maintenance of standing posture. Participants were asked to maintain the steady-state upright standing posture while pulling forces of different magnitudes were applied at the level at the waist in eight horizontal directions. Muscle synergies were extracted by nonnegative matrix factorization from sixteen lower limb and trunk muscles. An average of 5-6 muscle synergies were sufficient to account for a wide variety of EMG waveforms associated with changes in the magnitude and direction of pulling forces. A cluster analysis partitioned the muscle synergies of the participants into a large group of clusters according to their similarity, indicating the use of a subjective combination of muscles to generate a multidirectional force vector in standing. Furthermore, we found a participant-specific distribution in the values of cosine directional tuning parameters of synergy amplitude coefficients, suggesting the existence of individual neuromechanical strategies to stabilize the whole-body posture. Our findings provide a starting point for the development of novel diagnostic tools to assess muscle coordination in postural control and lay the foundation for potential applications of muscle synergies in rehabilitation.

show abstract

Postural response characterization of standing humans to multi-directional, predictable and unpredictable perturbations to the arm

Cited by 7 publications

References 28 publications

Short-latency muscle response patterns to multi-directional, unpredictable perturbations to balance applied to the arm are context dependent

Short-latency muscle response patterns to multi-directional, unpredictable perturbations to balance applied to the arm are context dependent

Stability of vertical posture explored with unexpected mechanical perturbations: synergy indices and motor equivalence

Muscle synergies for multidirectional isometric force generation during maintenance of upright standing posture

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