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Related Concept Videos

Muscle Stimulation Frequency01:22

Muscle Stimulation Frequency

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
At low firing rates, motor neurons induce individual twitch contractions in muscle fibers. These twitches...
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...
Relaxation of Skeletal Muscles01:29

Relaxation of Skeletal Muscles

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.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
Cross-bridge Cycle01:26

Cross-bridge Cycle

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.
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...
Muscle Recovery and Fatigue01:24

Muscle Recovery and Fatigue

Muscle fatigue refers to the decline in a muscle's ability to maintain the force of contraction after prolonged activity. It primarily stems from changes within muscle fibers. Even before experiencing muscle fatigue, one may feel tired and have the urge to stop the activity. This response, known as central fatigue, occurs due to changes in the central nervous system, namely the brain and spinal cord. While there is no single mechanism that induces fatigue, it may serve as a protective response...

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Related Experiment Video

Updated: Jun 20, 2026

Procedures for Rat in situ Skeletal Muscle Contractile Properties
09:49

Procedures for Rat in situ Skeletal Muscle Contractile Properties

Published on: October 15, 2011

The decrease in electrically evoked force production is delayed by a previous bout of stretch-shortening cycle

S Kamandulis1, A Skurvydas, N Masiulis

  • 1Human Motorics Laboratory, Lithuanian Academy of Physical Education, Sporto 6, LT-44221 Kaunas, Lithuania. s.kamandulis@lkka.lt

Acta Physiologica (Oxford, England)
|September 23, 2009
PubMed
Summary
This summary is machine-generated.

A prior bout of stretch-shortening cycle (SSC) exercise temporarily protects muscle function during a repeated exercise bout. This protective effect is evident during exercise and persists 24 hours later, though mechanisms may differ.

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Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies
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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

Related Experiment Videos

Last Updated: Jun 20, 2026

Procedures for Rat in situ Skeletal Muscle Contractile Properties
09:49

Procedures for Rat in situ Skeletal Muscle Contractile Properties

Published on: October 15, 2011

Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies
14:10

Isometric and Eccentric Force Generation Assessment of Skeletal Muscles Isolated from Murine Models of Muscular Dystrophies

Published on: January 31, 2013

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles
14:02

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

Published on: November 1, 2012

Area of Science:

  • Exercise physiology
  • Muscle biology
  • Sports science

Background:

  • Unaccustomed eccentric exercise causes muscle damage and reduced function, particularly at low frequencies.
  • Repeated bouts of eccentric exercise lead to reduced damage and faster recovery.
  • The protective effects of prior exercise on muscle function are not fully understood.

Purpose of the Study:

  • To test if prior stretch-shortening cycle (SSC) exercise protects against muscle function impairment during a subsequent SSC bout.
  • To determine if this protection is transient and diminishes as exercise progresses.

Main Methods:

  • Seven healthy untrained men performed 100 maximal drop jumps (SSC exercise) at 30-second intervals.
  • The same exercise protocol was repeated four weeks later.
  • Quadriceps muscle force (P15, P50) was measured pre-exercise, during exercise (10, 25, 50, 100 jumps), and 1, 24 hours post-exercise.

Main Results:

  • Peak muscle forces (P15, P50) were higher during the initial phase of the repeated bout compared to the first bout.
  • No significant difference in force was observed between bouts at the end of exercise.
  • Forces were again higher 24 hours after the repeated bout; the P15/P50 ratio was higher post-repeated bout.

Conclusions:

  • Prior SSC exercise provides temporary protection against impaired muscle contractile function during a repeated bout.
  • This protection is observable during exercise and also post-exercise, suggesting potentially different underlying mechanisms.