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Related Concept Videos

Motor Unit Stimulation01:20

Motor Unit Stimulation

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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...
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Muscle Stimulation Frequency01:22

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The contraction strength of muscles is regulated by motor neurons, which modulate the frequency of action potentials dispatched to the motor units based on the body's requirements. This process of varying the muscle stimulation frequency allows muscles to contract with a force that is precisely tailored to the needs of the moment, whether lifting a feather or a heavy box.
Wave summation
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Relaxation of Skeletal Muscles01:29

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The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions in the sarcoplasm, and the availability of energy or ATP to support contractions.
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As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.
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Excitation-Contraction Coupling in Skeletal Muscles01:20

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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.
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Smooth muscle contraction is a complex process vital for various bodily functions, from maintaining blood vessel tension to facilitating the movement of food through the digestive tract. Unlike striated muscles, smooth muscle contraction begins more slowly and lasts longer.
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Related Experiment Video

Updated: Mar 10, 2026

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles
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Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

Published on: November 1, 2012

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Changes in electromechanical delay during fatiguing dynamic muscle actions.

Cory M Smith1, Terry J Housh1, Ethan C Hill1

  • 1Department of Nutrition and Health Sciences, 110 Ruth Leverton Hall, University of Nebraska-Lincoln, Lincoln, Nebraska, 68583-0806, USA.

Muscle & Nerve
|December 10, 2016
PubMed
Summary
This summary is machine-generated.

Electromechanical delay (EMD) during leg extensions involves both excitation-contraction coupling and series elastic components. The series elastic component

Keywords:
electromyographyexcitation-contraction coupling failurefatiguemechanomyographyseries elastic component

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Area of Science:

  • Biomechanics
  • Exercise Physiology
  • Neuromuscular Function

Background:

  • Voluntary electromechanical delay (EMD) is a crucial factor in muscle force production.
  • Understanding the components contributing to EMD, such as excitation-contraction coupling and series elastic components, is vital for analyzing muscle performance.

Purpose of the Study:

  • To investigate the contributions of excitation-contraction coupling (EMDE-M) and the series elastic component (EMDM-F) to the overall electromechanical delay (EMDE-F) during fatiguing leg extensions.

Main Methods:

  • Twelve men performed submaximal leg extensions to failure at 30% of their 1-repetition maximum.
  • Onsets of electromyographic (EMG) signal, mechanomyographic (MMG) signal, and force production were measured.
  • EMDE-M, EMDM-F, and EMDE-F were assessed before, during, and after the fatiguing exercise bout.

Main Results:

  • Pretest and posttest assessments showed roughly equal contributions from EMDE-M and EMDM-F to the total EMDE-F.
  • During fatiguing exercise, increases in series elastic component compliance (affecting EMDM-F) began earlier (30% of repetitions) than excitation-contraction coupling failure (affecting EMDE-M, starting at 40%).

Conclusions:

  • The series elastic component significantly influences electromechanical delay during fatiguing contractions, preceding excitation-contraction coupling failure.
  • Both excitation-contraction coupling and series elastic components contribute to electromechanical delay throughout a fatiguing exercise bout.