The nervous system does not compensate for an acute change in the balance of passive force between synergist muscles

Lacourpaille, Lilian; Nordez, Antoine; Hug, François

doi:10.1242/jeb.163303

Cited by 10 publications

(14 citation statements)

References 46 publications

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“…2A). Large individual differences in EMG amplitude ratio already have been reported for knee extensors (14) and ankle plantar flexors (21). For example, Hug et al (14) reported a VL/VM activation ratio ranging from 33.6 to 74.7% during an isometric knee extension task performed at 20% of MVC, with an almost equal number of participants demonstrating either greater VL activation or greater VM activation.…”

Section: Individual Muscle Activation Strategiesmentioning

confidence: 95%

Coordination of hamstrings is individual specific and is related to motor performance

Avrillon

Guilhem

Barthélemy

et al. 2018

Journal of Applied Physiology

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The torque-sharing strategies between synergistic muscles may have important functional consequences. This study involved two experiments. The first experiment ( n = 22) aimed 1) to determine the relationship between the distribution of activation and the distribution of torque-generating capacity among the heads of the hamstring, and 2) to describe individual torque-sharing strategies and to determine whether these strategies are similar between legs. The second experiment ( n = 35) aimed to determine whether the distribution of activation between the muscle heads affects endurance performance during a sustained submaximal knee flexion task. Surface electromyography (EMG) was recorded from biceps femoris (BF), semimembranosus (SM), and semitendinosus (ST) during submaximal isometric knee flexions. Torque-generating capacity was estimated by measuring muscle volume, fascicle length, pennation angle, and moment arm. The product of the normalized EMG amplitude and the torque-generating capacity was used as an index of muscle torque. The distributions of muscle activation and of torque-generating capacity were not correlated significantly (all P> 0.18). Thus, there was a torque imbalance between the muscle heads (ST torque > BF and SM torque; P < 0.001), the magnitude of which varied greatly between participants. A significant negative correlation was observed between the imbalance of activation across the hamstring muscles and the time to exhaustion ( P < 0.001); i.e., the larger the imbalance of activation across muscles, the lower the muscle endurance performance. Torque-sharing strategies between the heads of the hamstrings are individual specific and related to muscle endurance performance. Whether these individual strategies play a role in hamstring injury remains to be determined. NEW & NOTEWORTHY The distribution of activation among the heads of the hamstring is not related to the distribution of torque-generating capacity. The torque-sharing strategies within hamstring muscles vary greatly between individuals but are similar between legs. Hamstring coordination affects endurance performance; i.e., the larger the imbalance of activation across the muscle heads, the lower the muscle endurance.

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Section: Individual Muscle Activation Strategiesmentioning

confidence: 95%

Coordination of hamstrings is individual specific and is related to motor performance

Avrillon

Guilhem

Barthélemy

et al. 2018

Journal of Applied Physiology

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“…Interestingly, previous studies examining the muscle shear modulus during contraction have reported a nonlinear response with contraction intensity (Bouillard et al 2012), and a heterogeneous shear modulus between synergistic muscles (Bouillard et al 2012;Lacourpaille et al 2017). The nonlinear response opposes what is expected with the myoelectric response (i.e., linear response) during an isometric contraction at a given joint angle (Kellis and Katis 2008;Campy et al 2009).…”

Section: Introductionmentioning

confidence: 91%

“…This has also recently been observed in vivo using SWE during a passive condition (i.e., no muscle contraction) (Umegaki et al 2015a, b;Le Sant et al 2015;Miyamoto et al 2017); while it has been shown that ST stiffness was the lowest among the hamstring muscles. However, measurements under passive conditions are unlikely to reflect the stiffness response during contraction (Shinohara et al 2010;Lacourpaille et al 2017). Therefore, the stiffness of each hamstring muscle during contraction remains to be examined in vivo.…”

Section: Introductionmentioning

confidence: 99%

Hamstring stiffness pattern during contraction in healthy individuals: analysis by ultrasound-based shear wave elastography

et al. 2018

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“…1B). As previous studies have shown differential changes in neural drive between GL and GM/SOL during constrained isometric plantarflexions (Lacourpaille et al, 2017;Hug et al, 2021a), we hypothesized that two main sources of common inputs may drive the triceps surae muscles during plantarflexion. Thus, we simulated 100 motor neurons receiving common and independent synaptic inputs using the model developed by Elias and Kohn (2013), with two compartments for the soma and the dendritic tree.…”

Section: Part 1: Simulationsmentioning

confidence: 99%

Two motor neuron synergies, invariant across ankle joint angles, activate the triceps surae during plantarflexion

Levine

Avrillon

Farina

et al. 2022

Preprint

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Recent studies have suggested that the central nervous system generates movements by controlling groups of motor neurons (synergies) that do not always align with muscle anatomy. In this study, we determined whether these synergies are robust across tasks with different mechanical constraints. We identified motor neuron synergies using principal component analysis (PCA) and cross-correlations between smoothed discharge rates of motor neurons. In Part 1, we used simulations to validate these methods. The results suggested that PCA can accurately identity the number of common inputs and classify motor neurons according to the synaptic weights of the common inputs they receive. Moreover, the results confirmed that cross-correlation can separate pairs of motor neurons that receive common inputs from those that do not receive common inputs. In Part 2, sixteen individuals performed plantarflexion at three ankle angles while recording high-density surface electromyography from the gastrocnemius lateralis (GL) and medialis (GM) and the soleus (SOL) muscles. We identified and tracked the same motor units across angles. PCA revealed two motor neuron synergies, primarily grouping motor neurons innervating GL-SOL and GM-SOL. These motor neuron synergies were relatively stable with 74.0% of motor neurons classified in the same synergy across angles. Cross-correlation demonstrated that only 13.9% of pairs of motor neurons maintained a non-significant level of correlation across angles, confirming the large presence of common inputs. Overall, these results highlighted the modularity of movement control at the motor neuron level, which may ensure a sensible reduction of computational resources for movement control.

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The nervous system does not compensate for an acute change in the balance of passive force between synergist muscles

Cited by 10 publications

References 46 publications

Coordination of hamstrings is individual specific and is related to motor performance

Coordination of hamstrings is individual specific and is related to motor performance

Hamstring stiffness pattern during contraction in healthy individuals: analysis by ultrasound-based shear wave elastography

Two motor neuron synergies, invariant across ankle joint angles, activate the triceps surae during plantarflexion

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