Simulating Motor Units for Fatigue Arm Muscles in Digital Humans

2006 ◽  
Author(s):  
Quanjia Yang ◽  
Ray P. S. Han ◽  
Laura Frey Law
Keyword(s):  
Motor Units ◽  
Digital Humans ◽  
Arm Muscles

Coordination and inhomogeneous activation of human arm muscles during isometric torques

1988 ◽  
Vol 60 (5) ◽  
pp. 1523-1548 ◽  
Author(s):  
E. J. van Zuylen ◽  
C. C. Gielen ◽  
J. J. Denier van der Gon
Keyword(s):  
Elbow Joint ◽  
Motor Units ◽  
Theoretical Models ◽  
Mechanical Action ◽  
Muscle Coordination ◽  
Mechanical Advantage ◽  
Elbow Angle ◽  
Flexion Extension ◽  
Arm Muscles ◽  
Extension Direction

1. In this study we have recorded the activity of motor units of the important muscles acting across the elbow joint during combinations of voluntary isometric torques in flexion/extension direction and supination/pronation direction at different angles of the elbow joint. 2. Most muscles are not activated homogeneously; instead the population of motor units of muscles can be subdivided into several subpopulations. Inhomogeneous activation of the population of motor units in a muscle is a general finding and is not restricted to some multifunctional muscles. 3. Muscles can be activated even if their mechanical action does not contribute directly to the external torque. For example, m. triceps is activated during supination torques and thus compensates for the flexion component of the m. biceps. On the other hand, motor units in muscles are not necessarily activated if their mechanical action contributes to a prescribed torque. For example, there are motor units in the m. biceps that are activated during flexion torques, but not during supination torques. 4. The relative activation of the muscles depends on the elbow angle. Changing the elbow angle affects the mechanical advantage of different muscles differently. In general, muscles with the larger mechanical advantage receive the larger input. 5. We have calculated the relative contributions of some muscles to isometric torques. These contributions depend on the combination of the torques exerted. 6. Existing theoretical models on muscle coordination do not incorporate subpopulations of motor units and therefore need to be amended.

What Can We Learn from Sarcopenia with Curarisation in the Context of Cancer Surgery? A Review of the Literature

2019 ◽  
Vol 25 (28) ◽  
pp. 3005-3010
Author(s):  
Georges Samouri ◽  
Alexandre Stouffs ◽  
Lionel V. Essen ◽  
Olivier Simonet ◽  
Marc De Kock ◽  
...  
Keyword(s):  
Frail Elderly ◽  
Muscle Fibers ◽  
Motor Units ◽  
The Elderly ◽  
Hepatic Function ◽  
Volume Of Distribution ◽  
Neuromuscular Blocking ◽  
Cancer Surgery ◽  
Old People ◽  
Age Related

Introduction: The monitoring of the curarisation is a unique opportunity to investigate the function of the neuromuscular junction (NMJ) during cancer surgery, especially in frailty-induced and age-related sarcopenia. Method: We conducted a comprehensive literature review in PubMed, without any limit of time related to frailty, sarcopenia, age and response to neuromuscular blockers in the context of cancer surgery. Results: Several modifications appear with age: changes in cardiac output, a decrease in muscle mass and increase in body fat, the deterioration in renal and hepatic function, the plasma clearance and the volume of distribution in elderly are smaller. These changes can be exacerbated in cancer patients. We also find modifications of the NMJ: dysfunctional mitochondria, modifications in the innervation of muscle fibers and motor units, uncoupling of the excitation-contraction of muscle fibers, inflammation. : Neuromuscular blocking agents (NMBAs) compete with acetylcholine and prevent it from fixing itself on its receptor. Many publications reported guidelines for using NMBAs in the elderly, based on studies comparing old people with young people. : No one screened frailty before, and thus, no studies compared frail elderly and non-frail elderly undergoing cancer surgery. Conclusion: Despite many studies about curarisation in the specific populations, and many arguments for a potential interest for investigation, no studies investigated specifically the response to NMBAs in regard of the frailty-induced and age-related sarcopenia.

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.

scholarly journals Axon typing of rat muscle nerves using a double staining procedure for cholinesterase and carbonic anhydrase.

1991 ◽  
Vol 39 (12) ◽  
pp. 1617-1625 ◽  
Author(s):  
M J Szabolcs ◽  
A Windisch ◽  
R Koller ◽  
M Pensch
Keyword(s):  
Carbonic Anhydrase ◽  
Cross Sections ◽  
Sensory Nerve ◽  
Histological Section ◽  
Trapezius Muscle ◽  
Motor Units ◽  
Conventional Technique ◽  
Nerve Fibers ◽  
Staining Procedure ◽  
Muscle Nerve

We developed a method for detecting activity of axonal cholinesterase (CE) and carbonic anhydrase (CA)--markers for motor and sensory nerve fibers (NFs)--in the same histological section. To reach this goal, cross-sections of muscle nerves were sequentially incubated with the standard protocols for CE and CA histochemistry. A modified incubation medium was used for CA in which Co++ is replaced by Ni++. This avoids interference of the two histochemical reactions because Co++ binds unspecifically to the brown copper-ferroferricyanide complex representing CE activity, whereas Ni++ does not. Cross-sections of the trapezius muscle nerve containing efferent and afferent NFs in segregated fascicles showed that CE activity was confined to motor NFs. Axonal CA was detected solely in sensory NFs. The number of labeled motor and sensory NFs determined in serial cross-sections stained with either the new or the conventional technique was not significantly different. Morphometric analysis revealed that small unreactive NFs (diameter less than 5 microns) are afferent, medium-sized ones (5 microns less than d less than 7 microns) are unclassifiable, and large ones (d greater than 7 microns) are efferent. The heterogenous CE activity of thick (alpha) motor NFs is linked to the type of their motor units. "Fast" motor units contain CE reactive NFs; "slow" ones have CE negative neurites.

scholarly journals Bioengineered model of the human motor unit with physiologically functional neuromuscular junctions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Rowan P. Rimington ◽  
Jacob W. Fleming ◽  
Andrew J. Capel ◽  
Patrick C. Wheeler ◽  
Mark P. Lewis
Keyword(s):  
Neuromuscular Junction ◽  
Motor Neuron ◽  
Motor Unit ◽  
Motor Nerve ◽  
Motor Units ◽  
Extracellular Matrices ◽  
Synaptic Membrane ◽  
Type I ◽  
Dependent Manner ◽  
Human Motor

AbstractInvestigations of the human neuromuscular junction (NMJ) have predominately utilised experimental animals, model organisms, or monolayer cell cultures that fail to represent the physiological complexity of the synapse. Consequently, there remains a paucity of data regarding the development of the human NMJ and a lack of systems that enable investigation of the motor unit. This work addresses this need, providing the methodologies to bioengineer 3D models of the human motor unit. Spheroid culture of iPSC derived motor neuron progenitors augmented the transcription of OLIG2, ISLET1 and SMI32 motor neuron mRNAs ~ 400, ~ 150 and ~ 200-fold respectively compared to monolayer equivalents. Axon projections of adhered spheroids exceeded 1000 μm in monolayer, with transcription of SMI32 and VACHT mRNAs further enhanced by addition to 3D extracellular matrices in a type I collagen concentration dependent manner. Bioengineered skeletal muscles produced functional tetanic and twitch profiles, demonstrated increased acetylcholine receptor (AChR) clustering and transcription of MUSK and LRP4 mRNAs, indicating enhanced organisation of the post-synaptic membrane. The number of motor neuron spheroids, or motor pool, required to functionally innervate 3D muscle tissues was then determined, generating functional human NMJs that evidence pre- and post-synaptic membrane and motor nerve axon co-localisation. Spontaneous firing was significantly elevated in 3D motor units, confirmed to be driven by the motor nerve via antagonistic inhibition of the AChR. Functional analysis outlined decreased time to peak twitch and half relaxation times, indicating enhanced physiology of excitation contraction coupling in innervated motor units. Our findings provide the methods to maximise the maturity of both iPSC motor neurons and primary human skeletal muscle, utilising cell type specific extracellular matrices and developmental timelines to bioengineer the human motor unit for the study of neuromuscular junction physiology.

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