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Wu CC, Lin YT, Hu CL, Chen YC, Hwang IS. Fatigue Alleviation by Low-Level Laser Preexposure in Ischemic Neuromuscular Electrical Stimulation. Med Sci Sports Exerc 2024; 56:1795-1804. [PMID: 38689440 DOI: 10.1249/mss.0000000000003472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/02/2024]
Abstract
PURPOSE Despite its susceptibility to muscle fatigue, combined neuromuscular electrical stimulation (NMES) and blood flow restriction (BFR) are effective regimens for managing muscle atrophy when traditional resistance exercises are not feasible. This study investigated the potential of low-level laser therapy (LLLT) in reducing muscle fatigue after the application of combined NMES and BFR. METHODS Thirty-six healthy adults were divided into control and LLLT groups. The LLLT group received 60 J of 850-nm wavelength LLLT before a training program of combined NMES and BFR of the nondominant extensor carpi radialis longus (ECRL). The control group followed the same protocol but received sham laser therapy. Assessments included maximal voluntary contraction, ECRL mechanical properties, and isometric force tracking for wrist extension. RESULTS The LLLT group exhibited a smaller normalized difference in maximal voluntary contraction decrement (-4.01 ± 4.88%) than the control group (-23.85 ± 7.12%) ( P < 0.001). The LLLT group demonstrated a smaller decrease in muscle stiffness of the ECRL compared with the control group, characterized by the smaller normalized changes in frequency ( P = 0.002), stiffness ( P = 0.002), and relaxation measures ( P = 0.011) of mechanical oscillation waves. Unlike the control group, the LLLT group exhibited a smaller posttest increase in force fluctuations during force tracking ( P = 0.014), linked to the predominant recruitment of low-threshold MU ( P < 0.001) without fatigue-related increases in the discharge variability of high-threshold MU ( P > 0.05). CONCLUSIONS LLLT preexposure reduces fatigue after combined NMES and BFR, preserving force generation, muscle stiffness, and force scaling. The functional benefits are achieved through fatigue-resistant activation strategies of motor unit recruitment and rate coding.
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Affiliation(s)
- Chia-Chan Wu
- Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan City, TAIWAN
| | - Yen-Ting Lin
- Department of Ball Sport, National Taiwan University of Sport, Taichung City, TAIWAN
| | - Chia-Ling Hu
- Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan City, TAIWAN
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De SD, Ambike S, Latash ML. Two aspects of feed-forward control of action stability: effects of action speed and unexpected events. Exp Brain Res 2024; 242:2177-2191. [PMID: 38992203 DOI: 10.1007/s00221-024-06892-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2024] [Accepted: 07/07/2024] [Indexed: 07/13/2024]
Abstract
We explored two types of anticipatory synergy adjustments (ASA) during accurate four-finger total force production task. The first type is a change in the index of force-stabilizing synergy during a steady state when a person is expecting a signal to produce a quick force change, which is seen even when the signal does not come (steady-state ASA). The other type is the drop in in the synergy index prior to a planned force change starting at a known time (transient ASA). The subjects performed a task of steady force production at 10% of maximal voluntary contraction (MVC) followed by a ramp to 20% MVC over 1 s, 3 s, and as a step function (0 s). In another task, in 50% of the trials during the steady-state phase, an unexpected signal could come requiring a quick force pulse to 20% MVC (0-surprise). Inter-trial variance in the finger force space was used to quantify the index of force-stabilizing synergy within the uncontrolled manifold hypothesis. We observed significantly lower synergy index values during the steady state in the 0-ramp trials compared to the 1-ramp and 3-ramp trials. There was also larger transient ASA during the 0-ramp trials. In the 0-surprise condition, the synergy index was significantly higher compared to the 0-ramp condition whereas the transient ASA was significantly larger. The finding of transient ASA scaling is of importance for clinical studies, which commonly involve populations with slower actions, which can by itself be associated with smaller ASAs. The participants varied the sharing pattern of total force across the fingers more in the task with "surprises". This was coupled to more attention to precision of performance, i.e., inter-trial deviations from the target as reflected in smaller variance affecting total force, possibly reflecting higher concentration on the task, which the participants perceived as more challenging compared to a similar task without surprise targets.
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Affiliation(s)
- Sayan Deep De
- Department of Kinesiology, The Pennsylvania State University, Rec.Hall-268N, University Park, PA, 16802, USA
| | - Satyajit Ambike
- Department of Health and Kinesiology, Purdue University, West Lafayette, IN, 47907, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, Rec.Hall-268N, University Park, PA, 16802, USA.
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Benamati A, Ricotta JM, De SD, Latash ML. Three Levels of Neural Control Contributing to Performance-stabilizing Synergies in Multi-finger Tasks. Neuroscience 2024; 551:262-275. [PMID: 38838976 DOI: 10.1016/j.neuroscience.2024.05.044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 05/28/2024] [Accepted: 05/30/2024] [Indexed: 06/07/2024]
Abstract
We tested a hypothesis on force-stabilizing synergies during four-finger accurate force production at three levels: (1) The level of the reciprocal and coactivation commands, estimated as the referent coordinate and apparent stiffness of all four fingers combined; (2) The level of individual finger forces; and (3) The level of firing of individual motor units (MU). Young, healthy participants performed accurate four-finger force production at a comfortable, non-fatiguing level under visual feedback on the total force magnitude. Mechanical reflections of the reciprocal and coactivation commands were estimated using small, smooth finger perturbations applied by the "inverse piano" device. Firing frequencies of motor units in the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC) were estimated using surface recording. Principal component analysis was used to identify robust MU groups (MU-modes) with parallel changes in the firing frequency. The framework of the uncontrolled manifold hypothesis was used to compute synergy indices in the spaces of referent coordinate and apparent stiffness, finger forces, and MU-mode magnitudes. Force-stabilizing synergies were seen at all three levels. They were present in the MU-mode spaces defined for MUs in FDS, in EDC, and pooled over both muscles. No effects of hand dominance were seen. The synergy indices defined at different levels of analysis showed no correlations across the participants. The findings are interpreted within the theory of control with spatial referent coordinates for the effectors. We conclude that force stabilization gets contributions from three levels of neural control, likely associated with cortical, subcortical, and spinal circuitry.
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Affiliation(s)
- Anna Benamati
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy; Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Joseph M Ricotta
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Sayan D De
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
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Marsala MJ, Gabriel DA, Greig Inglis J, Christie AD. How many motor units is enough? An assessment of the influence of the number of motor units on firing rate calculations. J Electromyogr Kinesiol 2024; 75:102872. [PMID: 38458102 DOI: 10.1016/j.jelekin.2024.102872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 02/25/2024] [Accepted: 03/02/2024] [Indexed: 03/10/2024] Open
Abstract
The number of motor units included in calculations of mean firing rates varies widely in the literature. It is unknown how the number of decomposed motor units included in the calculation of firing rate per participant compares to the total number of active motor units in the muscle, and if this is different for males and females. Bootstrapped distributions and confidence intervals (CI) of mean motor unit firing rates decomposed from the tibialis anterior were used to represent the total number of active motor units for individual participants in trials from 20 to 100 % of maximal voluntary contraction. Bootstrapped distributions of mean firing rates were constructed using different numbers of motor units, from one to the maximum number for each participant, and compared to the CIs. A probability measure for each number of motor units involved in firing rate was calculated and then averaged across all individuals. Motor unit numbers required for similar levels of probability increased as contraction intensity increased (p < 0.001). Increased levels of probability also required higher numbers of motor units (p < 0.001). There was no effect of sex (p ≥ 0.97) for any comparison. This methodology should be repeated in other muscles, and aged populations.
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Affiliation(s)
- Michael J Marsala
- School of Kinesiology, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada
| | - David A Gabriel
- Department of Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
| | - J Greig Inglis
- Department of Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
| | - Anita D Christie
- School of Kinesiology, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada.
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Weinman LE, Del Vecchio A, Mazzo MR, Enoka RM. Motor unit modes in the calf muscles during a submaximal isometric contraction are changed by brief stretches. J Physiol 2024; 602:1385-1404. [PMID: 38513002 DOI: 10.1113/jp285437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 02/29/2024] [Indexed: 03/23/2024] Open
Abstract
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. KEY 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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Affiliation(s)
- Logan E Weinman
- Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Alessandro Del Vecchio
- Department of Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University, Erlangen, Germany
| | - Melissa R Mazzo
- Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado, USA
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Marsala MJ, Christie AD. Neuromuscular behaviour in the first dorsal interosseus following mental fatigue. Exp Physiol 2024; 109:416-426. [PMID: 38130030 PMCID: PMC10988746 DOI: 10.1113/ep091349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 11/28/2023] [Indexed: 12/23/2023]
Abstract
We examined sex-specific changes to neuromuscular function in response to mental fatigue. Twenty-five young, healthy adults (13 F, 12 M) performed a mentally fatiguing task and control condition for 30 min on two separate days. Neuromuscular function was assessed in the first dorsal interosseous before and after each condition. Reaction time decreased after the mentally fatiguing task (P < 0.001, η2 = 0.47). Males and females reported higher levels of subjective fatigue after the mentally fatiguing task (P < 0.02, η2 = 0.07). Motor unit firing rate increased over time at 10% maximal voluntary contraction (MVC; P < 0.04, η2 = 0.16), and decreased over time at 50% MVC (P < 0.01, η2 = 0.14); however, this was not unique to either sex. During a variable force contraction, error decreased in females over time and increased in males (P < 0.05, η2 = 0.13), although changes were not unique to mental fatigue. Physiological function of the neuromuscular system was not specifically affected by mental fatigue in males or females.
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Affiliation(s)
- Michael J. Marsala
- School of Kinesiology, Faculty of Health SciencesThe University of Western OntarioOntarioCanada
| | - Anita D. Christie
- School of Kinesiology, Faculty of Health SciencesThe University of Western OntarioOntarioCanada
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7
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De SD, Ricotta JM, Benamati A, Latash ML. Two classes of action-stabilizing synergies reflecting spinal and supraspinal circuitry. J Neurophysiol 2024; 131:152-165. [PMID: 38116603 DOI: 10.1152/jn.00352.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 11/30/2023] [Accepted: 12/19/2023] [Indexed: 12/21/2023] Open
Abstract
We explored force-stabilizing synergies during accurate four-finger constant force production tasks in spaces of finger modes (commands to fingers computed to account for the finger interdependence) and of motor unit (MU) firing frequencies. The main specific hypothesis was that the multifinger synergies would disappear during unintentional force drifts without visual feedback on the force magnitude, whereas MU-based synergies would be robust to such drifts. Healthy participants performed four-finger accurate cyclical force production trials followed by trials of constant force production. Individual MUs were identified in the flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC). Principal component analysis was applied to motor unit frequencies to identify robust MU groups (MU-modes) with parallel scaling of the firing frequencies in FDS, in EDC, and the combined MUs of FDS + EDC. The framework of the uncontrolled manifold hypothesis was used to quantify force-stabilizing synergies when visual feedback on the force magnitude was available and 15 s after turning the visual feedback off. Removing visual feedback led to a force drift toward lower magnitudes, accompanied by the disappearance of multifinger synergies. In contrast, MU-mode synergies were minimally affected by removing visual feedback off and continued to be robust for the FDS and for the EDC, while being absent for the (FDS + EDC) analysis. We interpret the findings within the theory of hierarchical control of action with spatial referent coordinates. The qualitatively different behavior of the multifinger and MU-mode-based synergies likely reflects the difference in the involved neural circuitry, supraspinal for the former and spinal for the latter.NEW & NOTEWORTHY Two types of synergies, in the space of commands to individual fingers and in the space of motor unit groups, show qualitatively different behaviors during accurate multifinger force-production tasks. After removing visual feedback, finger force synergies disappear, whereas motor unit-based synergies persist. These results point at different neural circuitry involved in these two basic classes of synergies: supraspinal for multieffector synergies, and spinal for motor unit-based synergies.
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Affiliation(s)
- Sayan Deep De
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
| | - Joseph M Ricotta
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
| | - Anna Benamati
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
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Piscitelli D, Buttram A, Gibson S, Hager J, Thomas B, Solnik S. Test-Retest reliability and measurement error of the uncontrolled manifold analysis: A step towards the clinical translation. J Biomech 2024; 162:111902. [PMID: 38103314 DOI: 10.1016/j.jbiomech.2023.111902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Revised: 12/04/2023] [Accepted: 12/11/2023] [Indexed: 12/19/2023]
Abstract
The uncontrolled manifold (UCM) analysis has gained broad application in biomechanics and neuroscience for investigating the structure of motor variability in functional tasks. The UCM utilizes inter-trial analysis to partition the variance of elemental variables (e.g., finger forces, joint angles) that affect (VORT) and do not affect (VUCM) a performance variable (e.g., total force, end-effector position). However, to facilitate the translation of UCM into clinical settings, it is crucial to demonstrate the reliability of UCM estimates: VORT, VUCM, and their normalized difference, ΔV. This study aimed to determine the test-retest reliability using the intraclass correlation coefficient (ICC3,K), Bland-Altman plots, the standard error of measurement (SEM), and the minimal detectable change (MDC) of UCM estimate. Fifteen healthy individuals (24.8 ± 1.2 yrs old) performed a finger coordination task, with sessions separated by one hour, one day, and one week. Excellent reliability was found for VORT (ICC3,K = 0.97) and VUCM (ICC3,K = 0.92), whereas good reliability was observed for ΔV (ICC3,K = 0.84). Bland-Altman plots reveled no systematic differences. SEM% values were 24.57 %, 26.80 % and 12.49 % for VORT, VUCM and ΔV respectively, while the normalized MDC% values were 68.12 %, 74.30 % and 34.61 % for VORT, VUCM and ΔV respectively. Our results support the use of UCM as a reliable method for investigating the structure of movement variability. The excellent measurement properties make the UCM a promising tool for tracking changes in motor behavior over time (i.e., effects of interventions in prospective studies).
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Affiliation(s)
| | - Adrien Buttram
- Department of Physical Therapy, University of North Georgia, Dahlonega, GA, USA
| | - Stephanie Gibson
- Department of Physical Therapy, University of North Georgia, Dahlonega, GA, USA
| | - Joel Hager
- Department of Physical Therapy, University of North Georgia, Dahlonega, GA, USA
| | - Ben Thomas
- Department of Physical Therapy, University of North Georgia, Dahlonega, GA, USA
| | - Stanislaw Solnik
- Department of Physical Therapy, University of North Georgia, Dahlonega, GA, USA.
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Ricotta JM, De SD, Nardon M, Benamati A, Latash ML. Effects of fatigue on intramuscle force-stabilizing synergies. J Appl Physiol (1985) 2023; 135:1023-1035. [PMID: 37732378 DOI: 10.1152/japplphysiol.00419.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 08/22/2023] [Accepted: 09/14/2023] [Indexed: 09/22/2023] Open
Abstract
We applied the recently introduced concept of intramuscle synergies in spaces of motor units (MUs) to quantify indexes of such synergies in the tibialis anterior during ankle dorsiflexion force production tasks and their changes with fatigue. We hypothesized that MUs would be organized into robust groups (MU modes), which would covary across trials to stabilize force magnitude, and the indexes of such synergies would drop under fatigue. Healthy, young subjects (n = 15; 8 females) produced cyclical, isometric dorsiflexion forces while surface electromyography was used to identify action potentials of individual MUs. Principal component analysis was used to define MU modes. The framework of the uncontrolled manifold (UCM) was used to analyze intercycle variance and compute the synergy index, ΔVZ. Cyclical force production tasks were repeated after a nonfatiguing exercise (control) and a fatiguing exercise. Across subjects, fatigue led, on average, to a 43% drop in maximal force and fewer identified MUs per subject (29.6 ± 2.1 vs. 32.4 ± 2.1). The first two MU modes accounted for 81.2 ± 0.08% of variance across conditions. Force-stabilizing synergies were present across all conditions and were diminished after fatiguing exercise (1.49 ± 0.40) but not control exercise (1.76 ± 0.75). Decreased stability after fatigue was caused by an increase in the amount of variance orthogonal to the UCM. These findings contrast with earlier studies of multieffector synergies demonstrating increased synergy index under fatigue. We interpret the results as reflections of a drop in the gain of spinal reflex loops under fatigue. The findings corroborate an earlier hypothesis on the spinal nature of intramuscle synergies.NEW & NOTEWORTHY Across multielement force production tasks, fatigue of an element leads to increased indexes of force stability (synergy indexes). Here, however, we show that groups of motor units in the tibialis anterior show decreased indexes of force-stabilizing synergies after fatiguing exercise. These findings align intramuscle synergies with spinal mechanisms, in contrast to the supraspinal control of multimuscle synergies.
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Affiliation(s)
- Joseph M Ricotta
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
- Clinical and Translational Science Institute, Penn State College of Medicine, Hershey, Pennsylvania, United States
| | - Sayan D De
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
| | - Mauro Nardon
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Anna Benamati
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, Pennsylvania, United States
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Levine J, Avrillon S, Farina D, Hug F, Pons JL. Two motor neuron synergies, invariant across ankle joint angles, activate the triceps surae during plantarflexion. J Physiol 2023; 601:4337-4354. [PMID: 37615253 PMCID: PMC10952824 DOI: 10.1113/jp284503] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2023] [Accepted: 08/10/2023] [Indexed: 08/25/2023] Open
Abstract
Recent studies have suggested that the 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 identify the number of common inputs and their distribution across active motor neurons. 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, 16 individuals performed plantarflexion at three ankle angles while we recorded EMG signals from the gastrocnemius lateralis (GL) and medialis (GM) and the soleus (SOL) with grids of surface electrodes. The PCA revealed two motor neuron synergies. These motor neuron synergies were relatively stable, with no significant differences in the distribution of motor neuron weights across ankle angles (P = 0.62). When the cross-correlation was calculated for pairs of motor units tracked across ankle angles, we observed that only 13.0% of pairs of motor units from GL and GM exhibited significant correlations of their smoothed discharge rates across angles, confirming the low level of common inputs between these muscles. Overall, these results highlight the modularity of movement control at the motor neuron level, suggesting a sensible reduction of computational resources for movement control. KEY POINTS: The CNS might generate movements by activating groups of motor neurons (synergies) with common inputs. We show here that two main sources of common inputs drive the motor neurons innervating the triceps surae muscles during isometric ankle plantarflexions. We report that the distribution of these common inputs is globally invariant despite changing the mechanical constraints of the tasks, i.e. the ankle angle. These results suggest the functional relevance of the modular organization of the CNS to control movements.
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Affiliation(s)
- Jackson Levine
- Legs + Walking LabShirley Ryan AbilityLabChicagoILUSA
- Department of Physical Medicine and RehabilitationFeinberg School of MedicineNorthwestern UniversityChicagoILUSA
- Department of Biomedical EngineeringMcCormick School of EngineeringNorthwestern UniversityChicagoILUSA
| | - Simon Avrillon
- Legs + Walking LabShirley Ryan AbilityLabChicagoILUSA
- Department of Physical Medicine and RehabilitationFeinberg School of MedicineNorthwestern UniversityChicagoILUSA
- Department of BioengineeringFaculty of Engineering, Imperial College LondonLondonUK
| | - Dario Farina
- Department of BioengineeringFaculty of Engineering, Imperial College LondonLondonUK
| | - François Hug
- Université Côte d'Azur, LAMHESSNiceFrance
- School of Biomedical SciencesThe University of QueenslandSt LuciaQueenslandAustralia
| | - José L. Pons
- Legs + Walking LabShirley Ryan AbilityLabChicagoILUSA
- Department of Physical Medicine and RehabilitationFeinberg School of MedicineNorthwestern UniversityChicagoILUSA
- Department of Biomedical EngineeringMcCormick School of EngineeringNorthwestern UniversityChicagoILUSA
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11
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Chen Y, Hu CL, Hong CK, Hsu KL, Kuan FC, Chen WL, Su WR, Chen YC, Hwang IS. Deficits in neuromuscular control of increasing force in patients with chronic lateral epicondylitis. Front Physiol 2023; 14:1178557. [PMID: 37637142 PMCID: PMC10450945 DOI: 10.3389/fphys.2023.1178557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Accepted: 08/02/2023] [Indexed: 08/29/2023] Open
Abstract
Objective: This study investigated the neuromuscular control of increasing and releasing force in patients with chronic lateral epicondylitis (CLE). Methods: Fifteen patients with CLE (10 males, 5 females, 46.5 ± 6.3 years) and fifteen healthy participants (9 males, 6 females, 45.3 ± 2.5 years) participated in this study. In addition to power grip and maximal voluntary contraction (MVC) of wrist extension, force fluctuation dynamics and characteristics of inter-spike intervals (ISI) of motor units (MUs) with various recruitment thresholds in the extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL) during a designated force-tracking task with a trapezoidal target (0%-75%-0% MVC) were assessed. Results: Besides a smaller MVC of wrist extension, the patients exhibited significantly greater task errors (p = 0.007) and force fluctuations (p = 0.001) during force increment than the healthy counterparts. Nevertheless, no force variables significantly differed between groups during force release (p > 0.05). During force increment, the amplitudes of the motor unit action potential of the ECRB and ECRL muscles of the patients were smaller than those of the heathy counterparts (p < 0.001). The patient group also exhibited a higher percentage of motor units (MU) with lower recruitment threshold (<5% MVC) in the ECRL/ECRB muscles and a lower percentage of MU with higher recruitment threshold (>40% MVC) in the ECRB muscle, compared to the healthy group. During force increment, the patient group exhibited a higher rate of decrease in inter-spike intervals (ISIs) of motor units with lower recruitment thresholds (<10% MVC) in the ECRB and ECRL muscles, compared to the control group (p < 0.005). Conclusion: The patients with CLE exhibited more pronounced impairment in increasing force than in releasing force. This impairment in increasing force is attributed to deficits in tendon structure and degenerative changes in the larger motor units of the wrist extensors. To compensate for the neuromuscular deficits, the rate of progressive increase in discharge rate of the remaining smaller motor units (MUs) is enhanced to generate force. Significance: The deficits in neuromuscular control observed in CLE with degenerative changes cannot be fully explained by the experimental pain model, which predicts pain-related inhibition on low-threshold motor units.
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Affiliation(s)
- Yueh Chen
- Institute of Allied Health Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan
- Department of Orthopedics, Madou Sin-Lâu Hospital, Tainan, Taiwan
| | - Chia-Ling Hu
- Institute of Allied Health Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan
| | - Chih-Kai Hong
- Department of Orthopaedic Surgery, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan
| | - Kai-Lan Hsu
- Department of Orthopaedic Surgery, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan
| | - Fa-Chuan Kuan
- Department of Orthopaedic Surgery, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan
| | - Wei-Li Chen
- Department of Orthopedics, Madou Sin-Lâu Hospital, Tainan, Taiwan
| | - Wei-Ren Su
- Department of Orthopaedic Surgery, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan
- Musculoskeletal Research Center, Innovation Headquarter, National Cheng Kung University, Tainan, Taiwan
| | - Yi-Ching Chen
- Department of Physical Therapy, College of Medical Science and Technology, Chung Shan Medical University, Taichung, Taiwan
| | - Ing-Shiou Hwang
- Institute of Allied Health Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan
- Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan, Taiwan
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12
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Hug F, Avrillon S, Sarcher A, Del Vecchio A, Farina D. Correlation networks of spinal motor neurons that innervate lower limb muscles during a multi-joint isometric task. J Physiol 2023; 601:3201-3219. [PMID: 35772071 DOI: 10.1113/jp283040] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 06/22/2022] [Indexed: 11/08/2022] Open
Abstract
Movements are reportedly controlled through the combination of synergies that generate specific motor outputs by imposing an activation pattern on a group of muscles. To date, the smallest unit of analysis of these synergies has been the muscle through the measurement of its activation. However, the muscle is not the lowest neural level of movement control. In this human study (n = 10), we used a purely data-driven method grounded on graph theory to extract networks of motor neurons based on their correlated activity during an isometric multi-joint task. Specifically, high-density surface electromyography recordings from six lower limb muscles were decomposed into motor neurons spiking activity. We analysed these activities by identifying their common low-frequency components, from which networks of correlated activity to the motor neurons were derived and interpreted as networks of common synaptic inputs. The vast majority of the identified motor neurons shared common inputs with other motor neuron(s). In addition, groups of motor neurons were partly decoupled from their innervated muscle, such that motor neurons innervating the same muscle did not necessarily receive common inputs. Conversely, some motor neurons from different muscles-including distant muscles-received common inputs. The study supports the theory that movements are produced through the control of small numbers of groups of motor neurons via common inputs and that there is a partial mismatch between these groups of motor neurons and muscle anatomy. We provide a new neural framework for a deeper understanding of the structure of common inputs to motor neurons. KEY POINTS: A central and unresolved question is how spinal motor neurons are controlled to generate movement. We decoded the spiking activities of dozens of spinal motor neurons innervating six muscles during a multi-joint task, and we used a purely data-driven method grounded on graph theory to extract networks of motor neurons based on their correlated activity (considered as common input). The vast majority of the identified motor neurons shared common inputs with other motor neuron(s). Groups of motor neurons were partly decoupled from their innervated muscle, such that motor neurons innervating the same muscle did not necessarily receive common inputs. Conversely, some motor neurons from different muscles, including distant muscles, received common inputs. The study supports the theory that movement is produced through the control of groups of motor neurons via common inputs and that there is a partial mismatch between these groups of motor neurons and muscle anatomy.
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Affiliation(s)
- François Hug
- LAMHESS, Université Côte d'Azur, Nice, France
- Laboratory 'Movement, Interactions, Performance' (EA 4334), Nantes University, Nantes, France
- Institut Universitaire de France (IUF), Paris, France
| | - Simon Avrillon
- Legs + Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, IL, USA
- Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA
- Neuromechanics & Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London, UK
| | - Aurélie Sarcher
- Laboratory 'Movement, Interactions, Performance' (EA 4334), Nantes University, Nantes, France
| | - Alessandro Del Vecchio
- Neuromuscular Physiology and Neural Interfacing Group, Department of Artificial Intelligence in Biomedical Engineering, Faculty of Engineering, Erlangen-Nuremberg, Friedrich-Alexander University, Erlangen, Germany
| | - Dario Farina
- Neuromechanics & Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London, UK
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13
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Pan Z, Liu L, Li X, Ma Y. The Influence of Experience on Neuromuscular Control of the Body When Cutting at Different Angles. J Mot Behav 2023; 55:423-434. [PMID: 37263584 DOI: 10.1080/00222895.2023.2218821] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 05/09/2023] [Accepted: 05/22/2023] [Indexed: 06/03/2023]
Abstract
Cutting is an offensive technique commonly used in football and basketball to pass the opponent's defence by changing direction quickly in running. This paper aims to investigate the effect of experience and angle on the neuromuscular control strategies of the trunk and lower limbs during cutting. Non-negative matrix factorisation and K-means were used to extract muscle synergies (muscles that are activated in parallel) of 12 subjects with cut experience and 9 subjects without experience based on the sEMG signal collected from cutting at three cut angles (45°, 90°, and 135°), which was also mapped into the spinal motor output. Uncontrolled manifold analysis was used to establish the relationship between muscle synergies and COP. This study found that experienced subjects tended to use the lower limb muscles rather than the postural muscles as stabiliser muscles compared to novices. Experienced subjects can recruit an additional set of muscle synergy to cope with large-angle cuts. In addition, experienced subjects can activate the second muscle synergy, involving the hip and ankle stabilisation muscles, in advance to improve postural stability when cutting in large-angle. Synergy index of experienced subjects dropped rapidly before the quick stop and was relatively high during the change of direction. These results suggest that experience can modify the postural stabilisation mechanisms during cutting, and prompt the lower limb muscle synergy to produce anticipatory adjustment to improve postural stability in the anterior-posterior and internal-external directions.
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Affiliation(s)
- Zhengye Pan
- College of Physical Education and Sports, Beijing Normal University, Beijing, China
| | - Lushuai Liu
- College of Physical Education and Sports, Beijing Normal University, Beijing, China
| | - Xingman Li
- College of Physical Education and Sports, Beijing Normal University, Beijing, China
| | - Yunchao Ma
- College of Physical Education and Sports, Beijing Normal University, Beijing, China
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14
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Del Vecchio A, Marconi Germer C, Kinfe TM, Nuccio S, Hug F, Eskofier B, Farina D, Enoka RM. The Forces Generated by Agonist Muscles during Isometric Contractions Arise from Motor Unit Synergies. J Neurosci 2023; 43:2860-2873. [PMID: 36922028 PMCID: PMC10124954 DOI: 10.1523/jneurosci.1265-22.2023] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 02/03/2023] [Accepted: 02/12/2023] [Indexed: 03/17/2023] Open
Abstract
The purpose of our study was to identify the low-dimensional latent components, defined hereafter as motor unit modes, underlying the discharge rates of the motor units in two knee extensors (vastus medialis and lateralis, eight men) and two hand muscles (first dorsal interossei and thenars, seven men and one woman) during submaximal isometric contractions. Factor analysis identified two independent motor unit modes that captured most of the covariance of the motor unit discharge rates. We found divergent distributions of the motor unit modes for the hand and vastii muscles. On average, 75% of the motor units for the thenar muscles and first dorsal interosseus were strongly correlated with the module for the muscle in which they resided. In contrast, we found a continuous distribution of motor unit modes spanning the two vastii muscle modules. The proportion of the muscle-specific motor unit modes was 60% for vastus medialis and 45% for vastus lateralis. The other motor units were either correlated with both muscle modules (shared inputs) or belonged to the module for the other muscle (15% for vastus lateralis). Moreover, coherence of the discharge rates between motor unit pools was explained by the presence of shared synaptic inputs. In simulations with 480 integrate-and-fire neurons, we demonstrate that factor analysis identifies the motor unit modes with high levels of accuracy. Our results indicate that correlated discharge rates of motor units that comprise motor unit modes arise from at least two independent sources of common input among the motor neurons innervating synergistic muscles.SIGNIFICANCE STATEMENT It has been suggested that the nervous system controls synergistic muscles by projecting common synaptic inputs to the engaged motor neurons. In our study, we reduced the dimensionality of the output produced by pools of synergistic motor neurons innervating the hand and thigh muscles during isometric contractions. We found two neural modules, each representing a different common input, that were each specific for one of the muscles. In the vastii muscles, we found a continuous distribution of motor unit modes spanning the two synergistic muscles. Some of the motor units from the homonymous vastii muscle were controlled by the dominant neural module of the other synergistic muscle. In contrast, we found two distinct neural modules for the hand muscles.
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Affiliation(s)
- Alessandro Del Vecchio
- Department Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University, 91052 Erlangen, Germany
| | - Carina Marconi Germer
- Department of Bioengineering, Federal University of Pernambuco, CEP 50670-901 Recife, Brazil
| | - Thomas M Kinfe
- Division of Functional Neurosurgery and Stereotaxy, Friedrich-Alexander University, 91052 Erlangen, Germany
| | - Stefano Nuccio
- Department Human Movement Science, University of Rome Foro Italico, 00185 Rome, Italy
| | - François Hug
- Le Laboratoire Motricité Humaine Expertise Sport Santé, Université Côte d'Azur, 06103 Nice, France
| | - Bjoern Eskofier
- Department Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University, 91052 Erlangen, Germany
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado Boulder, Boulder, Colorado CO 80309
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15
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Hug F, Avrillon S, Ibáñez J, Farina D. Common synaptic input, synergies and size principle: Control of spinal motor neurons for movement generation. J Physiol 2023; 601:11-20. [PMID: 36353890 PMCID: PMC10098498 DOI: 10.1113/jp283698] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2022] [Accepted: 11/07/2022] [Indexed: 11/11/2022] Open
Abstract
Understanding how movement is controlled by the CNS remains a major challenge, with ongoing debate about basic features underlying this control. In current established views, the concepts of motor neuron recruitment order, common synaptic input to motor neurons and muscle synergies are usually addressed separately and therefore seen as independent features of motor control. In this review, we analyse the body of literature in a broader perspective and we identify a unified approach to explain apparently divergent observations at different scales of motor control. Specifically, we propose a new conceptual framework of the neural control of movement, which merges the concept of common input to motor neurons and modular control, together with the constraints imposed by recruitment order. This framework is based on the following assumptions: (1) motor neurons are grouped into functional groups (clusters) based on the common inputs they receive; (2) clusters may significantly differ from the classical definition of motor neuron pools, such that they may span across muscles and/or involve only a portion of a muscle; (3) clusters represent functional modules used by the CNS to reduce the dimensionality of the control; and (4) selective volitional control of single motor neurons within a cluster receiving common inputs cannot be achieved. Here, we discuss this framework and its underlying theoretical and experimental evidence.
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Affiliation(s)
- François Hug
- Université Côte d'Azur, LAMHESS, Nice, France.,School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Simon Avrillon
- Department of Bioengineering, Imperial College London, London, UK
| | - Jaime Ibáñez
- Department of Bioengineering, Imperial College London, London, UK.,BSICoS, IIS Aragón, Universidad de Zaragoza, Zaragoza, Spain.,Department for Clinical and movement neurosciences, Institute of Neurology, University College London, London, UK
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London, UK
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16
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Optimality, Stability, and Agility of Human Movement: New Optimality Criterion and Trade-Offs. Motor Control 2023; 27:123-159. [PMID: 35279021 DOI: 10.1123/mc.2021-0135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 01/20/2022] [Accepted: 02/05/2022] [Indexed: 12/31/2022]
Abstract
This review of movement stability, optimality, and agility is based on the theory of motor control with changes in spatial referent coordinates for the effectors, the principle of abundance, and the uncontrolled manifold hypothesis. A new optimality principle is suggested based on the concept of optimal sharing corresponding to a vector in the space of elemental variables locally orthogonal to the uncontrolled manifold. Motion along this direction is associated with minimal components along the relatively unstable directions within the uncontrolled manifold leading to a minimal motor equivalent motion. For well-practiced actions, this task-specific criterion is followed in spaces of referent coordinates. Consequences of the suggested framework include trade-offs among stability, optimality, and agility, unintentional changes in performance, hand dominance, finger specialization, individual traits in performance, and movement disorders in neurological patients.
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17
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Latash ML. The control and perception of antagonist muscle action. Exp Brain Res 2023; 241:1-12. [PMID: 36309879 DOI: 10.1007/s00221-022-06498-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2022] [Accepted: 10/20/2022] [Indexed: 01/26/2023]
Abstract
The review covers a range of topics related to the role of the antagonist muscles in agonist-antagonist pairs within the theory of the neural control of movements with spatial referent coordinates, the principle of abundance, and the uncontrolled manifold hypothesis. It starts with the mechanical role of the antagonist in stopping movements and providing necessary levels of effector mechanical characteristics for fast movements. Further, it discusses the role of antagonist muscle activation bursts during voluntary movements, force production, and postural tasks. Recent studies show that agonist and antagonist motor units are united into common groups related to two basic commands, reciprocal and coactivation. A number of phenomena are considered including intra-muscle synergies stabilizing net force production, unintentional force drifts during isometric force production, effects of voluntary muscle coactivation on force production and perception, and perceptual errors caused by various factors including lack of visual feedback and muscle vibration. Taken together, the findings suggest inherent instability of neural commands (time functions of the stretch reflex threshold) to antagonist muscles requiring visual information for accurate performance. They also suggest that neural commands to antagonist muscles are not readily incorporated into kinesthetic perception leading to illusions and errors in matching tasks.
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Affiliation(s)
- Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA, 16802, USA.
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18
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Intra-muscle Synergies Stabilizing Reflex-mediated Force Changes. Neuroscience 2022; 505:59-77. [DOI: 10.1016/j.neuroscience.2022.10.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Revised: 09/23/2022] [Accepted: 10/10/2022] [Indexed: 11/20/2022]
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19
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Aoyama T, Kohno Y. Differences in motor unit firing properties of the vastus lateralis muscle during postural and voluntary tasks. Front Physiol 2022; 13:955912. [PMID: 36246135 PMCID: PMC9561828 DOI: 10.3389/fphys.2022.955912] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2022] [Accepted: 09/13/2022] [Indexed: 11/13/2022] Open
Abstract
The firing properties of the motor units are usually affected by the motor task. However, it has not been clarified whether the firing properties of the motor units of a specific muscle are different between postural and voluntary tasks. Therefore, this study investigated whether the recruitment and rate coding of the motor units differ between these two motor tasks. Thirteen healthy volunteers performed trapezoidal muscle contraction with a target value of 15% maximum electromyography (EMG) activity by voluntary left knee extension in the sitting position (voluntary task) and postural maintenance in the semi-squatting position (postural task) with a knee flexion angle of 30°. We obtained four channels of surface EMG activity during each task from left vastus lateralis muscle. We extracted the firing properties of individual motor units using the EMG decomposition algorithm. The recruitment threshold and motor unit action potential amplitude were significantly lower in the postural task than in the voluntary task, and conversely, the mean firing rate was significantly higher. These results were explained by the preferential recruitment of motor units with higher recruitment threshold and amplitude in the voluntary task, while motor units with lower recruitment threshold and higher firing rate were preferentially recruited in the postural task. Preferential activation of fatigue-resistant motor units in the postural task is a reasonable strategy as it allows for sustained postural maintenance. We provide the first evidence that motor unit firing properties are clearly different between postural and voluntary tasks, even at the same muscle activity level.
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Affiliation(s)
- Toshiyuki Aoyama
- Department of Physical Therapy, Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan
- *Correspondence: Toshiyuki Aoyama,
| | - Yutaka Kohno
- Centre for Medical Sciences, Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan
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20
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Synergies Stabilizing Vertical Posture in Spaces of Control Variables. Neuroscience 2022; 500:79-94. [PMID: 35952997 DOI: 10.1016/j.neuroscience.2022.08.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 07/14/2022] [Accepted: 08/04/2022] [Indexed: 11/22/2022]
Abstract
In this study, we address the question: Can the central nervous system stabilize vertical posture in the abundant space of neural commands? We assume that the control of vertical posture is associated with setting spatial referent coordinates (RC) for the involved muscle groups, which translates into two basic commands, reciprocal and co-activation. We explored whether the two commands co-varied across trials to stabilize the initial postural state. Young, healthy participants stood quietly against an external horizontal load and were exposed to smooth unloading episodes. Linear regression between horizontal force and center of mass coordinate during the unloading phase was computed to define the intercept (RC) and slope (apparent stiffness, k). Hyperbolic regression between the intercept and slope across unloading episodes and randomization analysis both demonstrated high indexes of co-variation stabilizing horizontal force in the initial state. Higher co-variation indexes were associated with lower average k values across the participants suggesting destabilizing effects of muscle coactivation. Analysis of deviations in the {RC; k} space keeping the posture unchanged (motor equivalent) between two states separated by a voluntary quick body sway showed significantly larger motor equivalent deviations compared to non-motor equivalent ones. This is the first study demonstrating posture-stabilizing synergies in the space of neural control variables using various computational methods. It promises direct applications to studies of postural disorders and rehabilitation.
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21
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Moiseev SA, Pukhov AM, Mikhailova EA, Gorodnichev RM. Methodological and Computational Aspects of Extracting Extensive Muscle Synergies in Moderate-Intensity Locomotions. J EVOL BIOCHEM PHYS+ 2022. [DOI: 10.1134/s0022093022010094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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22
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Madarshahian S, Latash ML. Effects of hand muscle function and dominance on intra-muscle synergies. Hum Mov Sci 2022; 82:102936. [PMID: 35217391 DOI: 10.1016/j.humov.2022.102936] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 01/09/2022] [Accepted: 02/13/2022] [Indexed: 11/04/2022]
Abstract
The goal of the study was to explore the effects of hand dominance and muscle function (prime mover vs. supporting muscle) on recently discovered intra-muscle synergies as potential windows into their neural origin. Healthy right-handed subjects performed accurate cyclical force production tasks while pressing with the middle phalanges and distal phalanges of the fingers of the dominant and non-dominant hand. Surface electromyography was used to identify individual motor unit action potentials in two muscles, flexor digitorum superficialis (FDS) and extensor digitorum communis (EDC). Stable motor unit groups (MU-modes) were defined in each muscle and in both muscles together. The composition of the MU-modes allowed linking them to the reciprocal and co-activation command. Force-stabilizing synergies were quantified in each hand and during force production at both sites using the framework of the uncontrolled manifold hypothesis. Force-stabilizing synergies were seen in the spaces of MU-modes from FDS and EDC separately, but not of MU-modes defined for both muscles together. Synergy indices were similar for both hands and both sites of force application. In contrast, force-stabilizing synergies in the space of finger forces were present in the non-dominant hand and absent in the dominant hand. The data suggest existence of distributed mechanisms of synergic control. Finger force synergies are likely to reflect functioning of subcortical loops involving the basal ganglia and cerebellum, while MU-mode synergies are likely to reflect spinal circuitry. Studies of both force-based and motor-unit-based synergies may be clinically valuable for distinguishing effects of spinal and supraspinal disorders.
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Affiliation(s)
- Shirin Madarshahian
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA 16802, USA.
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23
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Intramuscle Synergies: Their Place in the Neural Control Hierarchy. Motor Control 2022; 27:402-441. [PMID: 36543175 DOI: 10.1123/mc.2022-0094] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 10/03/2022] [Accepted: 10/24/2022] [Indexed: 12/24/2022]
Abstract
We accept a definition of synergy introduced by Nikolai Bernstein and develop it for various actions, from those involving the whole body to those involving a single muscle. Furthermore, we use two major theoretical developments in the field of motor control—the idea of hierarchical control with spatial referent coordinates and the uncontrolled manifold hypothesis—to discuss recent studies of synergies within spaces of individual motor units (MUs) recorded within a single muscle. During the accurate finger force production tasks, MUs within hand extrinsic muscles form robust groups, with parallel scaling of the firing frequencies. The loading factors at individual MUs within each of the two main groups link them to the reciprocal and coactivation commands. Furthermore, groups are recruited in a task-specific way with gains that covary to stabilize muscle force. Such force-stabilizing synergies are seen in MUs recorded in the agonist and antagonist muscles but not in the spaces of MUs combined over the two muscles. These observations reflect inherent trade-offs between synergies at different levels of a control hierarchy. MU-based synergies do not show effects of hand dominance, whereas such effects are seen in multifinger synergies. Involuntary, reflex-based, force changes are stabilized by intramuscle synergies but not by multifinger synergies. These observations suggest that multifinger (multimuscle synergies) are based primarily on supraspinal circuitry, whereas intramuscle synergies reflect spinal circuitry. Studies of intra- and multimuscle synergies promise a powerful tool for exploring changes in spinal and supraspinal circuitry across patient populations.
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24
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Introduction to the Special Z-Issue in Honor of the 90th Birthday of Vladimir M. Zatsiorsky. Motor Control 2022; 27:1-5. [DOI: 10.1123/mc.2022-0118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Accepted: 10/04/2022] [Indexed: 11/11/2022]
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25
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Lara JE, Cheng LK, Rohrle O, Paskaranandavadivel N. Muscle-Specific High-Density Electromyography Arrays for Hand Gesture Classification. IEEE Trans Biomed Eng 2021; 69:1758-1766. [PMID: 34847014 DOI: 10.1109/tbme.2021.3131297] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
OBJECTIVE Dexterous hand motion is critical for object manipulation. Electrophysiological studies of the hand are key to understanding its underlying mechanisms. High-density electromyography (HD-EMG) provides spatio-temporal information about the underlying electrical activity of muscles, which can be used in neurophysiological research, rehabilitation and control applications. However, existing EMG electrodes platforms are not muscle-specific, which makes the assessment of intrinsic hand muscles difficult. METHODS Muscle-specific flexible HD-EMG electrode arrays were developed to capture intrinsic hand muscle myoelectric activity during manipulation tasks. The arrays consist of 60 individual electrodes targeting 10 intrinsic hand muscles. Myoelectric activity was displayed as spatio-temporal amplitude maps to visualize muscle activation. Time-domain and temporal-spatial HD-EMG features were extracted to train cubic support vector machine machine-learning classifiers to classify the intended user motion. RESULTS Experimental data was collected from 5 subjects performing a range of 10 common hand motions. Spatio-temporal EMG maps showed distinct activation areas correlated to the muscles recruited during each movement. The thenar muscle fiber conduction velocity (CV) was estimated to be at 4.70.3 m/s for all subjects. Hand motions were successfully classified and average accuracy for all subjects was directly related to spatial resolution based on the number of channels used as inputs; ranging from 744% when using only 5 channels and up to 922% when using 41 channels. Temporal-spatial features were shown to provide increased motion-specific accuracy when similar muscles were recruited for different gestures. CONCLUSIONS Muscle-specific electrodes were capable of accurately recording HD-EMG signals from intrinsic hand muscles and accurately predicting motion. SIGNIFICANCE The muscle-specific electrode arrays could improve electrophysiological research studies using EMG decomposition techniques to assess motor unit activity and in applications involving the analysis of dexterous hand motions.
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Latash ML. Understanding and Synergy: A Single Concept at Different Levels of Analysis? Front Syst Neurosci 2021; 15:735406. [PMID: 34867220 PMCID: PMC8636674 DOI: 10.3389/fnsys.2021.735406] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 11/01/2021] [Indexed: 11/15/2022] Open
Abstract
Biological systems differ from the inanimate world in their behaviors ranging from simple movements to coordinated purposeful actions by large groups of muscles, to perception of the world based on signals of different modalities, to cognitive acts, and to the role of self-imposed constraints such as laws of ethics. Respectively, depending on the behavior of interest, studies of biological objects based on laws of nature (physics) have to deal with different salient sets of variables and parameters. Understanding is a high-level concept, and its analysis has been linked to other high-level concepts such as "mental model" and "meaning". Attempts to analyze understanding based on laws of nature are an example of the top-down approach. Studies of the neural control of movements represent an opposite, bottom-up approach, which starts at the interface with classical physics of the inanimate world and operates with traditional concepts such as forces, coordinates, etc. There are common features shared by the two approaches. In particular, both assume organizations of large groups of elements into task-specific groups, which can be described with only a handful of salient variables. Both assume optimality criteria that allow the emergence of families of solutions to typical tasks. Both assume predictive processes reflected in anticipatory adjustments to actions (motor and non-motor). Both recognize the importance of generating dynamically stable solutions. The recent progress in studies of the neural control of movements has led to a theory of hierarchical control with spatial referent coordinates for the effectors. This theory, in combination with the uncontrolled manifold hypothesis, allows quantifying the stability of actions with respect to salient variables. This approach has been used in the analysis of motor learning, changes in movements with typical and atypical development and with aging, and impaired actions by patients with various neurological disorders. It has been developed to address issues of kinesthetic perception. There seems to be hope that the two counter-directional approaches will meet and result in a single theoretical scheme encompassing biological phenomena from figuring out the best next move in a chess position to activating motor units appropriate for implementing that move on the chessboard.
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Affiliation(s)
- Mark L. Latash
- Department of Kinesiology, The Pennsylvania State University, University Park, PA, United States
- Moscow Institute of Physics and Technology, Dolgoprudnyj, Russia
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27
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Madarshahian S, Latash ML. Reciprocal and coactivation commands at the level of individual motor units in an extrinsic finger flexor-extensor muscle pair. Exp Brain Res 2021; 240:321-340. [PMID: 34725732 DOI: 10.1007/s00221-021-06255-w] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 10/23/2021] [Indexed: 11/28/2022]
Abstract
We explored the synergic organization of motor units in extrinsic finger muscles, flexor digitorum superficialis (FDS), and extensor digitorum communis (EDC). Healthy subjects produced accurate cyclical force by pressing with the middle phalanges of one of the three fingers (Index, Middle, and Ring) and all three together. Two wireless sensor arrays were used to record and identify motor unit action potentials in FDS and EDC. Stable motor unit groups were identified within each muscle and across both muscles. Analysis of motor units combined over the two muscles showed one of the first two motor unit groups with consistently opposite signs of the loading factors for the FDS and EDC motor units, and the other group with consistently same signs of the loading factors for the two muscles. We interpret the two motor unit groups as reflections of the reciprocal and co-activation commands within the theory of control with spatial referent coordinates. Force changes within the cycle were primarily associated with the modulation of the co-activation motor unit group. Analysis of inter-cycle variance within the spaces of motor unit groups defined for FDS and EDC separately showed force-stabilizing synergies across both single-finger and three-finger tasks. In contrast, analysis within the motor unit groups defined across both muscles failed to show force-stabilizing synergies. We interpret these results as a reflection of the trade-off across levels within a hierarchical control system.
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Affiliation(s)
- Shirin Madarshahian
- Department of Kinesiology, The Pennsylvania State University, Rec.Hall-267, University Park, PA, 16802, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, Rec.Hall-267, University Park, PA, 16802, USA.
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Latash ML, Yamagata M. Recent Advances in the Neural Control of Movements: Lessons for Functional Recovery. Phys Ther Res 2021; 25:1-11. [PMID: 35582118 PMCID: PMC9095426 DOI: 10.1298/ptr.r0018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 07/12/2021] [Indexed: 09/05/2023]
Abstract
We review the current views on the control and coordination of movements following the traditions set by Nikolai Bernstein. In particular, we focus on the theory of neural control of effectors - from motor units to individual muscles, to joints, limbs, and to the whole body - with spatial referent coordinates organized into a hierarchy with multiple few-to-many mappings. Further, we discuss synergies ensuring stability of natural human movements within the uncontrolled manifold hypothesis. Synergies are organized within the neural control hierarchy based on the principle of motor abundance. Movement disorders are discussed as consequences of an inability to use the whole range of changes in referent coordinates (as in spasticity) and an inability to ensure controlled stability of salient variables as reflected in indices of multi-element synergies and their adjustments in preparation to actions (as in brain disorders, including Parkinson's disease, multiple-system atrophy, and stroke). At the end of the review, we discuss possible implications of this theoretical approach to peripheral disorders and their rehabilitations using, as an example, osteoarthritis. In particular, "joint stiffening" is viewed as a maladaptive strategy, which can compromise stability of salient variables during walking.
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Affiliation(s)
- Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, USA
| | - Momoko Yamagata
- Department of Human Development, Graduate School of Human Development and Environment, Kobe University, Japan
- Department of Physical Therapy, Human Health Science, Graduate School of Medicine, Kyoto University, Japan
- Research Fellow of the Japan Society for the Promotion of Science, Japan
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The Nature of Finger Enslaving: New Results and Their Implications. Motor Control 2021; 25:680-703. [PMID: 34530403 DOI: 10.1123/mc.2021-0044] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2021] [Revised: 07/01/2021] [Accepted: 07/25/2021] [Indexed: 11/18/2022]
Abstract
We present a review on the phenomenon of unintentional finger action seen when other fingers of the hand act intentionally. This phenomenon (enslaving) has been viewed as a consequence of both peripheral (e.g., connective tissue links and multifinger muscles) and neural (e.g., projections of corticospinal pathways) factors. Recent studies have shown relatively large and fast drifts in enslaving toward higher magnitudes, which are not perceived by subjects. These and other results emphasize the defining role of neural factors in enslaving. We analyze enslaving within the framework of the theory of motor control with spatial referent coordinates. This analysis suggests that unintentional finger force changes result from drifts of referent coordinates, possibly reflecting the spread of cortical excitation.
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Latash ML. One more time about motor (and non-motor) synergies. Exp Brain Res 2021; 239:2951-2967. [PMID: 34383080 DOI: 10.1007/s00221-021-06188-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 08/03/2021] [Indexed: 11/28/2022]
Abstract
We revisit the concept of synergy based on the recently translated classical book by Nikolai Bernstein (On the construction of movements, Medgiz, Moscow 1947; Latash, Bernstein's Construction of Movements, Routledge, Abingdon 2020b) and progress in understanding the physics and neurophysiology of biological action. Two aspects of synergies are described: organizing elements into stable groups (modes) and ensuring dynamical stability of salient performance variables. The ability of the central nervous system to attenuate synergies in preparation for a quick action-anticipatory synergy adjustments-is emphasized. Recent studies have demonstrated synergies at the level of hypothetical control variables associated with spatial referent coordinates for effectors. Overall, the concept of synergies fits naturally the hierarchical scheme of control with referent coordinates with an important role played by back-coupling loops within the central nervous system and from peripheral sensory endings. Further, we review studies showing non-trivial changes in synergies with development, aging, fatigue, practice, and a variety of neurological disorders. Two aspects of impaired synergic control-impaired stability and impaired agility-are introduced. The recent generalization of the concept of synergies for non-motor domains, including perception, is discussed. We end the review with a list of unresolved and troubling issues.
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Affiliation(s)
- Mark L Latash
- Department of Kinesiology, Rec.Hall-268N, The Pennsylvania State University, University Park, PA, 16802, USA.
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Tanzarella S, Muceli S, Santello M, Farina D. Synergistic Organization of Neural Inputs from Spinal Motor Neurons to Extrinsic and Intrinsic Hand Muscles. J Neurosci 2021; 41:6878-6891. [PMID: 34210782 PMCID: PMC8360692 DOI: 10.1523/jneurosci.0419-21.2021] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 06/02/2021] [Accepted: 06/03/2021] [Indexed: 11/21/2022] Open
Abstract
Our current understanding of synergistic muscle control is based on the analysis of muscle activities. Modules (synergies) in muscle coordination are extracted from electromyographic (EMG) signal envelopes. Each envelope indirectly reflects the neural drive received by a muscle; therefore, it carries information on the overall activity of the innervating motor neurons. However, it is not known whether the output of spinal motor neurons, whose number is orders of magnitude greater than the muscles they innervate, is organized in a low-dimensional fashion when performing complex tasks. Here, we hypothesized that motor neuron activities exhibit a synergistic organization in complex tasks and therefore that the common input to motor neurons results in a large dimensionality reduction in motor neuron outputs. To test this hypothesis, we factorized the output spike trains of motor neurons innervating 14 intrinsic and extrinsic hand muscles and analyzed the dimensionality of control when healthy individuals exerted isometric forces using seven grip types. We identified four motor neuron synergies, accounting for >70% of the variance of the activity of 54.1 ± 12.9 motor neurons, and we identified four functionally similar muscle synergies. However, motor neuron synergies better discriminated individual finger forces than muscle synergies and were more consistent with the expected role of muscles actuating each finger. Moreover, in a few cases, motor neurons innervating the same muscle were active in separate synergies. Our findings suggest a highly divergent net neural inputs to spinal motor neurons from spinal and supraspinal structures, contributing to the dimensionality reduction captured by muscle synergies.SIGNIFICANCE STATEMENT We addressed whether the output of spinal motor neurons innervating multiple hand muscles could be accounted for by a modular organization, i.e., synergies, previously described to account for the coordination of multiple muscles. We found that motor neuron synergies presented similar dimensionality (implying a >10-fold reduction in dimensionality) and structure as muscle synergies. Nonetheless, the synergistic behavior of subsets of motor neurons within a muscle was also observed. These results advance our understanding of how neuromuscular control arises from mapping descending inputs to muscle activation signals. We provide, for the first time, insights into the organization of neural inputs to spinal motor neurons which, to date, has been inferred through analysis of muscle synergies.
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Affiliation(s)
- Simone Tanzarella
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Silvia Muceli
- Division of Signal Processing and Biomedical Engineering, Department of Electrical Engineering, Chalmers University of Technology, Gothenburg 412 96, Sweden
| | - Marco Santello
- School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona 85287-9709
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
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Madarshahian S, Latash ML. Synergies at the level of motor units in single-finger and multi-finger tasks. Exp Brain Res 2021; 239:2905-2923. [PMID: 34312703 DOI: 10.1007/s00221-021-06180-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Accepted: 07/13/2021] [Indexed: 10/20/2022]
Abstract
We explored the organization of motor units recorded in the flexor digitorum superficialis into stable groups (MU-modes) and force-stabilizing synergies in spaces of MU-modes. Young, healthy participants performed one-finger and three-finger accurate cyclical force production tasks. Two wireless sensor arrays (Trigno Galileo, Delsys, Inc.) were placed over the proximal and distal portions of the muscle for surface recording and identification of motor unit action potentials. Principal component analysis with Varimax rotation and factor extraction was used to identify MU-modes. The framework of the uncontrolled manifold hypothesis was used to analyze inter-cycle variance in the space of MU-modes and compute the index of force-stabilizing synergy. Multiple linear regression between the first MU-mode in the three-finger task and the first MU-modes in the three single-finger tasks showed no differences between the data recorded by the two electrodes suggesting that MU-modes were unlikely to be synonymous with muscle compartments. Multi-MU-mode synergies stabilizing task force were documented across all tasks. In contrast, there were no force-stabilizing synergies in the three-finger task analyzed in the space of individual finger forces. Our results confirm the synergic organization of motor units in single-finger tasks and, for the first time, expand this result to multi-finger tasks. We offer an interpretation of the findings within the theoretical scheme of control with spatial referent coordinates expanded to the analysis of individual motor units. The results confirm trade-offs between synergies at different hierarchical levels and expand this notion to intra-muscle synergies.
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Affiliation(s)
- Shirin Madarshahian
- Department of Kinesiology, The Pennsylvania State University, Rec. Hall-267, University Park, PA, 16802, USA
| | - Mark L Latash
- Department of Kinesiology, The Pennsylvania State University, Rec. Hall-267, University Park, PA, 16802, USA.
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Optimality and stability of human behavior: Reply to comments on "Laws of nature that define biological action and perception". Phys Life Rev 2021; 38:145-149. [PMID: 34088609 DOI: 10.1016/j.plrev.2021.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 04/15/2021] [Indexed: 11/24/2022]
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Santello M. Pushing the boundaries of a physical approach for the study of sensorimotor control: Comment on "Laws of nature that define biological action and perception" by Mark L. Latash. Phys Life Rev 2021; 37:7-9. [PMID: 33676230 DOI: 10.1016/j.plrev.2021.02.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Accepted: 02/18/2021] [Indexed: 01/29/2023]
Affiliation(s)
- Marco Santello
- School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ 85287-9709, USA.
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