Synergies at the level of motor units in single-finger and multi-finger tasks

Madarshahian, Shirin; Latash, Mark L.

doi:10.1007/s00221-021-06180-y

Cited by 26 publications

(19 citation statements)

References 70 publications

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“…(2023) identified modes derived from the discharge times of motor units in tibialis anterior during isometric contractions and found that they were able to ensure dynamical stability when participants performed a cyclical force‐tracking task. This finding was interpreted as evidence for the possibility of synergistic control at the level of motor unit modes (Madarshahian & Latash 2022).…”

Section: Introductionmentioning

confidence: 91%

“…In the Bernstein tradition, however, one of the key criteria for a synergy is that it must ensure task‐specific stability; which is represented by consistent patterns of activation across trials to achieve the goal of the task (Madarshahian & Latash, 2022; Madarshahian et al., 2021). Until that criterion can be demonstrated, the low‐dimensional latent components extracted from the discharge times of motor units are more appropriately referred to as motor unit modes or modules (Del Vecchio et al., 2023; Hug et al., 2023; Madarshahian & Latash 2022; Madarshahian et al., 2021). As an example of motor unit modes that met the stability criterion, Ricotta, De, et al.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, the motor unit modes extracted from the thigh muscles failed to meet the criterion of a stable group of elements. In contrast, 77% of the motor units in first dorsal interosseus and 96% in thenar muscles remained in the same motor unit mode across trials, but these modes would need to be capable of ensuring dynamical stability before they could be classified as a synergy based on the Bernstein criteria (Madarshahian & Latash, 2022; Madarshahian et al., 2021). Similarly, Levine et al.…”

Section: Introductionmentioning

confidence: 99%

“…In the Bernstein tradition, however, one of the key criteria for a synergy is that it must ensure task-specific stability; which is represented by consistent patterns of activation across trials to achieve the goal of the task (Madarshahian & Latash, 2022;Madarshahian et al, 2021). Until that criterion can be demonstrated, the low-dimensional latent components extracted from the discharge times of motor units are more appropriately referred to as motor unit modes or modules (Del Vecchio et al, 2023;Hug et al, 2023;Madarshahian & Latash 2022;Madarshahian et al, 2021). As an example of motor unit modes that met the stability criterion, and identified modes derived from the discharge times of motor units in tibialis anterior during isometric contractions and found that they were able to ensure dynamical stability when participants performed a cyclical force-tracking task.…”

Section: Introductionmentioning

confidence: 99%

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Motor unit modes in the calf muscles during a submaximal isometric contraction are changed by brief stretches

Weinman,

Del Vecchio,

Mazzo

et al. 2024

The Journal of Physiology

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The purpose of our study was to investigate the influence of a stretch intervention on the common modulation of discharge rate among motor units in the calf muscles during a submaximal isometric contraction. The current report comprises a computational analysis of a motor unit dataset that we published previously (Mazzo et al., 2021). Motor unit activity was recorded from the three main plantar flexor muscles while participants performed an isometric contraction at 10% of the maximal voluntary contraction force before and after each of two interventions. The interventions were a control task (standing balance) and static stretching of the plantar flexor muscles. A factorization analysis on the smoothed discharge rates of the motor units from all three muscles yielded three modes that were independent of the individual muscles. The composition of the modes was not changed by the standing‐balance task, whereas the stretching exercise reduced the average correlation in the second mode and increased it in the third mode. A centroid analysis on the correlation values showed that most motor units were associated with two or three modes, which were presumed to indicate shared synaptic inputs. The percentage of motor units adjacent to the seven centroids changed after both interventions: Control intervention, mode 1 decreased and the shared mode 1 + 2 increased; stretch intervention, shared modes either decreased (1 + 2) or increased (1 + 3). These findings indicate that the neuromuscular adjustments during both interventions were sufficient to change the motor unit modes when the same task was performed after each intervention. imageKey points Based on covariation of the discharge rates of motor units in the calf muscles during a submaximal isometric contraction, factor analysis was used to assign the correlated discharge trains to three motor unit modes. The motor unit modes were determined from the combined set of all identified motor units across the three muscles before and after each participant performed a control and a stretch intervention. The composition of the motor unit modes changed after the stretching exercise, but not after the control task (standing balance). A centroid analysis on the distribution of correlation values found that most motor units were associated with a shared centroid and this distribution, presumably reflecting shared synaptic input, changed after both interventions. Our results demonstrate how the distribution of multiple common synaptic inputs to the motor neurons innervating the plantar flexor muscles changes after a brief series of stretches.

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Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Motor unit modes in the calf muscles during a submaximal isometric contraction are changed by brief stretches

Weinman,

Del Vecchio,

Mazzo

et al. 2024

The Journal of Physiology

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show abstract

“…However, the CST seems to be just as effective as principal component analysis in estimating the CoV for force (42). Alternatively, perhaps motor neuron pools receive more than one source of common input even during isometric contractions, which will require an approach at the level of neural modules (43,44).…”

Section: Mvc Forcementioning

confidence: 99%

Leg Dominance Does Not Influence Maximal Force, Force Steadiness, or Motor Unit Discharge Characteristics

Petrović

Amiridis

Holobar

et al. 2022

Medicine &Amp; Science in Sports &Amp; Exercise

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Purpose: The aim of our study was to compare maximal force, force steadiness, and discharge characteristics of motor units in tibialis anterior during contractions with the dorsiflexors of the dominant and nondominant legs at low-to-moderate target forces and three ankle angles. Methods: Twenty young adults performed maximal and submaximal isometric contractions (5%, 10%, 20%, 40%, and 60% of maximal voluntary contraction (MVC)) with the dorsiflexors of the dominant and nondominant legs at three ankle angles (75°, short length; 90°, intermediate length; 105°, long length). High-density EMG signals from the tibialis anterior muscle of each leg were recorded. Results: Maximal force (average dominant, 182.9 ± 64.5 N; nondominant, 179.0 ± 58.8 N) and the fluctuations in force, quantified as absolute (SD) and normalized amplitudes (coefficient of variation (CoV)), were similar between the two legs across the three ankle angles (average CoV for dominant, 1.5% ± 1.0%; nondominant, 1.7% ± 1.3%). The CoV for force for both legs decreased from 5% to 20% MVC force, and then it plateaued at 40% and 60% MVC force. EMG amplitude, mean discharge rate of motor units, discharge variability (interspike interval), and the variability in neural drive (filtered cumulative spike train) were similar between the two legs across the submaximal contractions. Conclusions: MVC force and force steadiness were similar across ankle angles and target forces between the dominant and nondominant legs. The attributes that underlie the self-reported identification of a dominant leg were not associated with the force capacity or the control of force for the dorsiflexor muscles, at least during isometric contractions.

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One more time about motor (and non-motor) synergies

Latash

2021

Exp Brain Res

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Synergies at the level of motor units in single-finger and multi-finger tasks

Cited by 26 publications

References 70 publications

Motor unit modes in the calf muscles during a submaximal isometric contraction are changed by brief stretches

Motor unit modes in the calf muscles during a submaximal isometric contraction are changed by brief stretches

Leg Dominance Does Not Influence Maximal Force, Force Steadiness, or Motor Unit Discharge Characteristics

One more time about motor (and non-motor) synergies

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