Force Steadiness: From Motor Units to Voluntary Actions

Enoka, Roger M.; Farina, Dario

doi:10.1152/physiol.00027.2020

Cited by 92 publications

(138 citation statements)

References 144 publications

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“…In recent years, decomposition of a surface EMG into contributions of individual MUs enabled analysis of neural coding in relatively large populations of MUs, and, consequentially, many new insights into the neurophysiology of the motor system [1], [3]- [8]. However identification of individual MUs from a surface EMG is not a trivial task.…”

Section: Introductionmentioning

confidence: 99%

On the Reuse of Motor Unit Filters in High Density Surface Electromyograms Recorded at Different Contraction Levels

Frančič

Holobar

2021

IEEE Access

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We analyzed the efficiency of Motor Unit (MU) tracking across different experimentally recorded contraction levels of Biceps Brachii (BB), Tibialis Anterior (TA), First Dorsal Interosseous (FDI) and Abductor Digiti Minimi (ADM) muscles and in simulated conditions. We used the Convolution Kernel Compensation (CKC) algorithm to estimate the MU filters from high-density electromyograms (HDEMGs) at contraction levels ranging from 5 % to 70 % of Maximum Voluntary Contraction (MVC), and applied these MU filters to all the recorded contractions levels of the same muscle. For each MU filter estimation-application pair we assessed the number of identified MUs, Pulse-to-Noise Ratio (PNR), Mean Discharge Rate (MDR) and MUAP peak-to-peak (P2P) amplitude, normalized by HDEMG P2P amplitude. In simulated conditions, we also calculated the Precision (P r) and Sensitivity (Se) of MU firing identification. We also reported the number of jointly identified MUs for all possible contraction level pairs. The results in simulated conditions confirmed the efficiency of MU filter transfer from low to high contraction levels. The large majority of MUs identified at lower contraction levels were tracked successfully at higher contraction levels, though many of them were not directly identified at higher contraction levels. Sensitivities of identified MU firings were above 97 %, decreasing only by about 1 % when transferring the MU filters from low to high contraction levels. In the experimental conditions the efficiency of the MU tracking depended significantly on the investigated muscle. The highest efficiency was demonstrated in the FDI muscle, where about 90 % and 70 % of MUs identified at the contraction level of MU filter estimation were also tracked at 10 % and 20 % higher contraction level, respectively. These figures decreased to 47 % and 20 % of MUs in TA, and to 21 % and 18 % of MUs in the BB muscle. The observed differences between the MU filter transfer efficiencies are likely caused by the differences in the size and anatomy of the investigated muscles.

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Section: Introductionmentioning

confidence: 99%

On the Reuse of Motor Unit Filters in High Density Surface Electromyograms Recorded at Different Contraction Levels

Frančič

Holobar

2021

IEEE Access

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“…Our results revealed that the CoV of force was smaller (better force steadiness) at the longer length (75 °) than at the shorter length (105 °) of the muscle-tendon unit. Force fluctuations are influenced by the amplitude of the low-frequency oscillations in the neural drive to muscle and the number of MUs, the upper limit of MU recruitment, and their contractile properties [2]. Although MVC force was substantially less at the shorter than the longer length, the target forces were specified relative to the MVC force at each ankle angle.…”

Section: Ankle Angle Did Influence Force Steadinessmentioning

confidence: 99%

“…However, the amplitude of force fluctuations is also influenced by the number of MUs, the upper limit of MU recruitment, and the contractile properties of the MUs [5][6][7]. When several muscles are contributing to the applied force, the amplitude of the force fluctuations depends on the collective properties of these muscles, including the proportion of shared synaptic inputs received by the pools of motor neurons [2].…”

Section: Introductionmentioning

confidence: 99%

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Ankle Angle but Not Knee Angle Influences Force Fluctuations During Plantar Flexion

et al. 2021

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The purpose of the study was to evaluate the influence of changes in ankle- and knee-joint angles on force steadiness and the discharge characteristics of motor units (MU) in soleus when the plantar flexors performed steady isometric contractions. Submaximal contractions (5, 10, 20, and 40% of maximum) were performed at two ankle angles (75° and 105°) and two knee angles (120° and 180°) by 14 young adults. The coefficient of variation of force decreased as the target force increased from 5 to 20% of maximal force, then remained unaltered at 40%. Independently of knee angle, the coefficient of variation for force at the ankle angle of 75° (long length) was always less (p<0.05) than that at 105° (shorter length). Mean discharge rate, discharge variability, and variability in neural activation of soleus motor units were less (p<0.05) at the 75° angle than at 105°. It was not possible to record MUs from medial gastrocnemius at the knee angle of 120° due to its minimal activation. The changes in knee-joint angle did not influence any of the outcome measures. The findings underscore the dominant role of the soleus muscle in the control of submaximal forces produced by the plantar flexor muscles.

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“…When attempting to sustain an isometric contraction, the applied force is never constant but rather fluctuates around an average value (as reviewed in Enoka and Farina, 2021). Typically, force variability is quantified over an entire isometric contraction, usually maintained over several seconds (Laidlaw et al, 2000;Jones et al, 2002;Tracy and Enoka, 2002;Ushiyama et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Temporally stable beta sensorimotor oscillations and cortico–muscular coupling underlie force steadiness

Mongold

Piitulainen

Legrand

et al. 2021

Preprint

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As humans, we seamlessly hold objects in our hands, and may even lose consciousness of these objects. This phenomenon raises the unsettled question of the involvement of the cerebral cortex, the core area for voluntary motor control, in dynamically maintaining steady muscle force. To address this issue, we measured magnetoencephalographic brain activity from healthy adults who maintained a steady pinch grip. Using a novel analysis approach, we uncovered fine-grained temporal modulations in the ∼20-Hz sensorimotor brain rhythm and its coupling with muscle activity, with respect to several aspects of muscle force (rate of increase/decrease or plateauing high/low). These modulations preceded changes in force features by ∼40 ms and possessed behavioral relevance, as less salient or absent modulation predicted a more stable force output. These findings have consequences for the existing theories regarding the functional role of cortico-muscular coupling, and suggest that steady muscle contractions are characterized by a stable rather than fluttering involvement of the sensorimotor cortex.

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Force Steadiness: From Motor Units to Voluntary Actions

Cited by 92 publications

References 144 publications

On the Reuse of Motor Unit Filters in High Density Surface Electromyograms Recorded at Different Contraction Levels

On the Reuse of Motor Unit Filters in High Density Surface Electromyograms Recorded at Different Contraction Levels

Ankle Angle but Not Knee Angle Influences Force Fluctuations During Plantar Flexion

Temporally stable beta sensorimotor oscillations and cortico–muscular coupling underlie force steadiness

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