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Related Concept Videos

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.
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The primary role of cardiac muscles is to propel blood throughout the cardiovascular system. The cardiac muscle cells, or cardiomyocytes, exhibit specialized characteristics that allow them to perform this function.
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Exercise induces a range of adaptations in muscle tissue, depending on the type and duration of activity. Such physical training can be broadly categorized into two types: endurance exercises and resistance exercises.
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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.
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Skeletal muscles continuously produce ATP to provide the energy that enables muscle contractions. Skeletal muscle fibers can be categorized into three types based on differences in their contraction speed and how they produce ATP, as well as physical differences related to these factors. Most human muscles contain all three muscle fiber types, albeit in varying proportions.
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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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Muscle strength, not age, explains unique variance in echo intensity.

Akash U Bali1, Kylie K Harmon1, Adam M Burton2

  • 1Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, USA; School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, USA.

Experimental Gerontology
|August 11, 2020
PubMed
Summary

Muscle strength is a better predictor of echo intensity (EI), a measure of skeletal muscle quality, than chronological age. This finding highlights the importance of assessing muscle strength when evaluating muscle health using EI.

Keywords:
Cross-sectional areaEcho intensityForceMuscle qualityRectus femorisSarcopeniaSubcutaneous adipose tissue thicknessTorqueUltrasoundVastus lateralis

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Area of Science:

  • Skeletal muscle physiology
  • Biomedical imaging
  • Gerontology

Background:

  • Echo intensity (EI) is increasingly used to assess skeletal muscle quality.
  • Previous research indicates independent associations between EI and both age and muscle strength.

Purpose of the Study:

  • To determine whether EI is more strongly associated with age or muscle strength.
  • To compare the predictive power of age versus muscle strength on EI.

Main Methods:

  • B-mode ultrasonography was used to image the vastus lateralis and rectus femoris muscles in 28 younger and 25 older adults.
  • ImageJ software quantified corrected EI and muscle cross-sectional area (CSA).
  • Maximal concentric isokinetic knee extensor strength and fatigability were measured; specific torque was calculated.

Main Results:

  • Significant differences in strength and CSA were observed between age groups.
  • Corrected EI showed minimal differences between age groups after accounting for subcutaneous tissue.
  • Stepwise regression identified muscle strength as the sole significant predictor of EI (R² = 0.206).

Conclusions:

  • Concentric isokinetic muscle strength is a superior predictor of echo intensity compared to age.
  • Muscle strength is a more critical determinant of skeletal muscle quality assessed by EI than age.