Motor unit recruitment and rate coding in response to fatiguing shoulder abductions and subsequent recovery

2000 ◽  
Vol 83 (2-3) ◽  
pp. 190-199 ◽  
Author(s):  
B. R. Jensen ◽  
M. Pilegaard ◽  
G. Sjøgaard
Keyword(s):  
Motor Unit ◽  
Motor Unit Recruitment ◽  
Subsequent Recovery ◽  
Rate Coding

scholarly journals The increase in muscle force after 4 weeks of strength training is mediated by adaptations in motor unit recruitment and rate coding

2019 ◽  
Vol 597 (7) ◽  
pp. 1873-1887 ◽  
Author(s):  
Alessandro Del Vecchio ◽  
Andrea Casolo ◽  
Francesco Negro ◽  
Matteo Scorcelletti ◽  
Ilenia Bazzucchi ◽  
...  
Keyword(s):  
Strength Training ◽  
Motor Unit ◽  
Muscle Force ◽  
Motor Unit Recruitment ◽  
Rate Coding

scholarly journals Integration of neural architecture within a finite element framework for improved neuromusculoskeletal modeling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Victoria L. Volk ◽  
Landon D. Hamilton ◽  
Donald R. Hume ◽  
Kevin B. Shelburne ◽  
Clare K. Fitzpatrick
Keyword(s):  
Finite Element ◽  
Motor Unit ◽  
Muscle Activation ◽  
Computational Models ◽  
Integrated Model ◽  
Motor Unit Recruitment ◽  
Average Error ◽  
Neural Architecture ◽  
Rate Coding ◽  
Musculoskeletal Systems

AbstractNeuromusculoskeletal (NMS) models can aid in studying the impacts of the nervous and musculoskeletal systems on one another. These computational models facilitate studies investigating mechanisms and treatment of musculoskeletal and neurodegenerative conditions. In this study, we present a predictive NMS model that uses an embedded neural architecture within a finite element (FE) framework to simulate muscle activation. A previously developed neuromuscular model of a motor neuron was embedded into a simple FE musculoskeletal model. Input stimulation profiles from literature were simulated in the FE NMS model to verify effective integration of the software platforms. Motor unit recruitment and rate coding capabilities of the model were evaluated. The integrated model reproduced previously published output muscle forces with an average error of 0.0435 N. The integrated model effectively demonstrated motor unit recruitment and rate coding in the physiological range based upon motor unit discharge rates and muscle force output. The combined capability of a predictive NMS model within a FE framework can aid in improving our understanding of how the nervous and musculoskeletal systems work together. While this study focused on a simple FE application, the framework presented here easily accommodates increased complexity in the neuromuscular model, the FE simulation, or both.

Neural control of the healthy pectoralis major from low-to-moderate isometric contractions

2021 ◽  
Author(s):  
Tea Lulic-Kuryllo ◽  
Christopher K. Thompson ◽  
ning.jiang Jiang ◽  
Francesco Negro ◽  
Clark Dickerson
Keyword(s):  
Motor Unit ◽  
Neural Control ◽  
Discharge Rate ◽  
Arm Movement ◽  
Shoulder Function ◽  
Pectoralis Major ◽  
Motor Unit Recruitment ◽  
Isometric Contractions ◽  
Motor Unit Discharge ◽  
Rate Coding

The pectoralis major critically enables arm movement in several directions. However, its neural control remains unknown. High-density electromyography (HD-sEMG) was acquired from the pectoralis major in two sets of experiments in healthy young adults. Participants performed ramp-and-hold isometric contractions in: adduction, internal rotation, flexion, and horizontal adduction at three force levels: 15%, 25%, and 50% scaled to task-specific maximal voluntary force (MVF). HD-sEMG signals were decomposed into motor unit spike trains using a convolutive blind source separation algorithm and matched across force levels using a motor unit matching algorithm. The mean discharge rate and coefficient of variation were quantified across the hold and compared between 15% and 25% MVF across all tasks, while comparisons between 25 and 50% MVF were made where available. Mean motor unit discharge rate was not significantly different between 15% and 25% MVF (all p > 0.05) across all tasks or between 25% and 50% MVF in horizontal adduction (p = 0.11), indicating an apparent saturation across force levels and the absence of rate coding. These findings suggest that the pectoralis major likely relies on motor unit recruitment to increase force, providing first-line evidence of motor unit recruitment in this muscle and paving the way for more deliberate investigations of the pectoralis major involvement in shoulder function.

Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG

2006 ◽  
Vol 100 (6) ◽  
pp. 1928-1937 ◽  
Author(s):  
Kevin G. Keenan ◽  
Dario Farina ◽  
Roberto Merletti ◽  
Roger M. Enoka
Keyword(s):  
Motor Unit ◽  
Conduction Velocity ◽  
Motor Units ◽  
Surface Emg ◽  
Excitation Level ◽  
Bipolar Electrode ◽  
Emg Signal ◽  
Motor Unit Synchronization ◽  
Rate Coding ◽  
Simulated Surface

The purpose of the study was to evaluate the influence of selected physiological parameters on amplitude cancellation in the simulated surface electromyogram (EMG) and the consequences for spike-triggered averages of motor unit potentials derived from the interference and rectified EMG signals. The surface EMG was simulated from prescribed recruitment and rate coding characteristics of a motor unit population. The potentials of the motor units were detected on the skin over a hand muscle with a bipolar electrode configuration. Averages derived from the EMG signal were generated using the discharge times for each of the 24 motor units with lowest recruitment thresholds from a population of 120 across three conditions: 1) excitation level; 2) motor unit conduction velocity; and 3) motor unit synchronization. The area of the surface-detected potential was compared with potentials averaged from the interference, rectified, and no-cancellation EMGs. The no-cancellation EMG comprised motor unit potentials that were rectified before they were summed, thereby preventing cancellation between the opposite phases of the potentials. The percent decrease in area of potentials extracted from the rectified EMG was linearly related to the amount of amplitude cancellation in the interference EMG signal, with the amount of cancellation influenced by variation in excitation level and motor unit conduction velocity. Motor unit synchronization increased potentials derived from both the rectified and interference EMG signals, although cancellation limited the increase in area for both potentials. These findings document the influence of amplitude cancellation on motor unit potentials averaged from the surface EMG and the consequences for using the procedure to characterize motor unit properties.

Determining patterns of motor recruitment during locomotion

2002 ◽  
Vol 205 (3) ◽  
pp. 359-369 ◽  
Author(s):  
James M. Wakeling ◽  
Motoshi Kaya ◽  
Genevieve K. Temple ◽  
Ian A. Johnston ◽  
Walter Herzog
Keyword(s):  
Motor Unit ◽  
Frequency Band ◽  
Fibre Type ◽  
Low Frequency ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Medial Gastrocnemius ◽  
Fibre Types ◽  
Myoelectric Signals ◽  
Frequency Bands

SUMMARY Motor units are the functional units of muscle contraction in vertebrates. Each motor unit comprises muscle fibres of a particular fibre type and can be considered as fast or slow depending on its fibre-type composition. Motor units are typically recruited in a set order, from slow to fast, in response to the force requirements from the muscle. The anatomical separation of fast and slow muscle in fish permits direct recordings from these two fibre types. The frequency spectra from different slow and fast myotomal muscles were measured in the rainbow trout Oncorhynchus mykiss. These two muscle fibre types generated distinct low and high myoelectric frequency bands. The cat paw-shake is an activity that recruits mainly fast muscle. This study showed that the myoelectric signal from the medial gastrocnemius of the cat was concentrated in a high frequency band during paw-shake behaviour. During slow walking, the slow motor units of the medial gastrocnemius are also recruited, and this appeared as increased muscle activity within a low frequency band. Therefore, high and low frequency bands could be distinguished in the myoelectric signals from the cat medial gastrocnemius and probably corresponded, respectively, to fast and slow motor unit recruitment. Myoelectric signals are resolved into time/frequency space using wavelets to demonstrate how patterns of motor unit recruitment can be determined for a range of locomotor activities.

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