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Related Concept Videos

Motor Unit Stimulation01:20

Motor Unit Stimulation

When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
Excitation-Contraction Coupling in Skeletal Muscles01:20

Excitation-Contraction Coupling in Skeletal Muscles

Excitation-contraction coupling is a series of events that occur between generating an action potential and initiating a muscle contraction. It occurs at the triad, a structure found in skeletal muscle fibers that comprise a T-tubule and terminal cisternae of the sarcoplasmic reticulum on each side. These triads are visible in longitudinally sectioned muscle fibers. They are typically located at the A-I junction — the junction between the A and I bands of the sarcomere.
When an action potential...
Myasthenia Gravis: Diagnostic Tests01:15

Myasthenia Gravis: Diagnostic Tests

Myasthenia gravis is an autoimmune condition affecting neuromuscular transmission, causing generalized weakness in skeletal muscles. Initial diagnoses rely on patients' signs, symptoms, and medical history. The challenge lies in distinguishing myasthenia from other muscular dystrophies. An important diagnostic feature is the significant improvement of symptoms after administering anticholinesterase inhibitors.
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Generation of Action Potential in Skeletal Muscles01:24

Generation of Action Potential in Skeletal Muscles

Every cell in the body maintains a membrane potential due to an uneven distribution of positive and negative charges across its plasma membrane. The membrane potential is measured in millivolts and quantifies the difference in charge across the membrane.
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Muscle Contraction01:15

Muscle Contraction

Muscle Contraction01:10

Muscle Contraction

In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate—the point of synaptic communication between motor neurons and muscle fibers. The binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle...

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Updated: May 21, 2026

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation
07:53

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Published on: September 13, 2015

A simple test of muscle coactivation estimation using electromyography.

U F Ervilha1, T Graven-Nielsen, M Duarte

  • 1Laboratório de Biodinâmica do Movimento Humano, Escola de Educação Física, Universidade São Judas Tadeu, São Paulo, SP, Brasil.

Brazilian Journal of Medical and Biological Research = Revista Brasileira De Pesquisas Medicas E Biologicas
|May 30, 2012
PubMed
Summary

Reliably estimating muscle coactivation using electromyography (EMG) requires specific normalization. Normalizing EMG signals by maximal voluntary contraction during coactivation improves accuracy, yielding results closer to the true value.

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Area of Science:

  • Biomechanics
  • Neuroscience
  • Kinesiology

Background:

  • Muscles coactivate to produce opposing torques during motor tasks.
  • Electromyography (EMG) signals are used to quantify muscle coactivation.
  • Reliable estimation of muscle coactivation using EMG indexes remains a challenge.

Purpose of the Study:

  • To assess the reliability of muscle coactivation estimation using electromyography (EMG).
  • To compare the performance of two different coactivation indexes.
  • To evaluate the impact of various EMG amplitude normalization procedures.

Main Methods:

  • Isometric coactivation tasks were performed at varying muscle activation levels.
  • Two coactivation indexes were calculated: (1) antagonistic activity divided by the mean of agonistic and antagonistic activity, and (2) the ratio of antagonistic to agonistic activity.
  • Indexes were computed using different EMG amplitude normalization methods, including normalization by maximal voluntary contraction.

Main Results:

  • The first index, normalized by maximal voluntary coactivation, yielded the most accurate coactivation estimation (92 ± 6%), closely approximating the true value.
  • The second index, without normalization, resulted in a significantly lower coactivation value (82 ± 12%).
  • Normalization by maximal voluntary contraction during coactivation is crucial for reliable EMG-based coactivation assessment.

Conclusions:

  • Muscle coactivation is most reliably estimated when EMG signals are normalized by their maximal voluntary contraction achieved during maximal coactivation.
  • This normalization method, applied to the first index, provides a more accurate measure of true coactivation.
  • The findings offer a refined approach for quantifying muscle coactivation in motor control research.