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Related Concept Videos

Alterations in Muscle Tone lll01:11

Alterations in Muscle Tone lll

Rigidity and myotonia are distinct abnormalities of muscle tone that affect resistance and relaxation during movement. Although both involve altered muscle contraction, they arise from different neurological and muscular mechanisms.CharacteristicsRigidity is characterized by uniform resistance to passive movement across the entire range, independent of speed, affecting flexors and extensors equally. It may appear as lead-pipe rigidity (smooth, constant resistance) or cogwheel rigidity...
Alterations in Muscle Tone ll01:12

Alterations in Muscle Tone ll

Alterations in muscle tone are common manifestations of neurological disorders and reflect dysfunction within different nervous system regions. Spasticity, paratonia, and dystonia represent distinct forms of hypertonia, each with unique mechanisms, clinical features, and diagnostic importance.CharacteristicsSpasticity happens from upper motor neuron lesions and is characterized by velocity-dependent resistance to passive movement. Clinical features include:Exaggerated deep tendon reflexesClonus...
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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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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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Isotonic and Isometric Muscle Contractions01:22

Isotonic and Isometric Muscle Contractions

Two primary types of muscle contractions are isotonic and isometric, each serving unique functions and involving distinct mechanisms. Both isotonic and isometric contractions are integral to the body's complex system of movement and stability. Isotonic exercises contribute significantly to functional strength and movement, while isometric contractions are crucial for maintaining posture and joint stability.
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Updated: Jul 15, 2026

Force and Position Control in Humans - The Role of Augmented Feedback
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Published on: June 19, 2016

Aging Alters Force Control Regularity and Delays Adaptation to Isometric Force Perturbations.

Stylianos Grigoriadis1, Vasileios Mylonas2, Vassilios Panoutsakopoulos1

  • 1Biomechanics Laboratory, School of Physical Education & Sport Science at Thessaloniki, Aristotle University of Thessaloniki, Thessaloniki, Greece.

Journal of Motor Behavior
|July 14, 2026
PubMed
Summary

Older adults take longer to adapt to force changes and show more regular force output than younger adults. This suggests aging impacts motor control adaptability, with force regularity being a key indicator.

Keywords:
adaptationentropyhand grip strengthvariability

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Last Updated: Jul 15, 2026

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Application of Chronic Stimulation to Study Contractile Activity-induced Rat Skeletal Muscle Phenotypic Adaptations

Published on: January 25, 2018

Area of Science:

  • Motor Control
  • Human Physiology
  • Aging Research

Background:

  • Variability in human force output is crucial for understanding motor control.
  • In young adults, force variability indicates efficient motor behavior.
  • Aging may impair neuromuscular adaptability, affecting responses to external disturbances.

Purpose of the Study:

  • To investigate age-related differences in motor control adaptability using a perturbation-based paradigm.
  • To quantify the time needed to recover baseline force after unexpected perturbations in young and older adults.
  • To assess how aging affects force regularity and variability magnitude during isometric grip tasks.

Main Methods:

  • Employed a perturbation-based paradigm involving isometric grip tasks with sudden upward and downward force changes.
  • Quantified adaptation time to return to baseline force following perturbations.
  • Assessed force regularity using Sample Entropy (SaEn) and variability magnitude using standard deviation (SD) across various contraction intensities (5-80% MVC).
  • Included 16 young and 18 older adults in the study.

Main Results:

  • Older adults demonstrated significantly longer adaptation times compared to young adults.
  • Older adults exhibited greater force regularity (higher SaEn) than young adults.
  • No significant difference in force variability magnitude (SD) was observed between age groups.
  • Downward perturbations led to slower force recovery than upward perturbations across both groups.

Conclusions:

  • Aging prolongs adaptation time and increases force output regularity, indicating reduced neuromuscular adaptability.
  • Perturbation-based assessments are sensitive tools for evaluating adaptive motor control in aging.
  • Force regularity emerges as a more sensitive marker of aging-related motor control changes than variability magnitude.