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Related Concept Videos

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...
Indirect Motor Pathways01:22

Indirect Motor Pathways

The indirect motor or extrapyramidal pathways originate in the brainstem, the lower portion of the brain that connects it to the spinal cord. They consist of several distinct tracts, each with specialized functions. The four main tracts of the indirect motor pathways are the vestibulospinal tract, the reticulospinal tract, the tectospinal tract, and the rubrospinal tract.
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Muscle Coordination and Action01:24

Muscle Coordination and Action

Muscle coordination is a complex and finely tuned process essential for smooth and purposeful movements like flexion, extension, adduction, abduction, and rotation. The human body orchestrates the actions of various muscles working in concert, each with a specific role. Four functional types describe how muscles work together: agonist, antagonist, synergist, and fixator.
Agonists
Agonist muscles, often called prime movers, are the primary muscles responsible for producing a specific movement.
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.
Isotonic contractions
Isotonic contractions occur when a muscle changes length while the...
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...
Somatic Spinal Reflexes01:22

Somatic Spinal Reflexes

Somatic spinal reflexes are rapid, involuntary muscular responses to external stimuli that involve the somatic musculature and the spinal cord.
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Related Experiment Video

Updated: Jun 27, 2026

Experimental Methods to Study Human Postural Control
08:12

Experimental Methods to Study Human Postural Control

Published on: September 11, 2019

Paradoxical muscle movement during postural control.

Ian David Loram1, Constantinos N Maganaris, Martin Lakie

  • 1Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Manchester, UK. i.loram@mmu.ac.uk

Medicine and Science in Sports and Exercise
|December 19, 2008
PubMed
Summary
This summary is machine-generated.

Human standing relies on calf muscles, but paradoxical movements challenge traditional balance control theories. New research shows muscle movements are often opposite to body sway, questioning the role of stretch reflexes.

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Last Updated: Jun 27, 2026

Experimental Methods to Study Human Postural Control
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Method to Measure Tone of Axial and Proximal Muscle
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Evaluating Postural Control and Lower-extremity Muscle Activation in Individuals with Chronic Ankle Instability
07:52

Evaluating Postural Control and Lower-extremity Muscle Activation in Individuals with Chronic Ankle Instability

Published on: September 18, 2020

Area of Science:

  • Biomechanics
  • Human Physiology
  • Motor Control

Background:

  • Human standing involves whole-body sway regulated by calf muscles.
  • Ankle stiffness and muscle stretch reflexes were traditionally thought crucial for maintaining upright stance.
  • This suggested calf muscles stretch and activate during forward sway to maintain balance.

Purpose of the Study:

  • To investigate the dynamic relationship between calf muscle contractile displacement and body sway during human standing.
  • To challenge traditional models of postural control based on ankle stiffness and stretch reflexes.
  • To explore the implications of observed muscle movements for balance regulation.

Main Methods:

  • Utilized a novel ultrasound technique to dynamically measure calf muscle contractile displacements.
  • Recorded and analyzed whole-body sway during undisturbed human standing.
  • Correlated calf muscle movements with body sway patterns.

Main Results:

  • Calf muscle contractile displacement was poorly or negatively correlated with body sway.
  • Observed 'paradoxical muscle movements' where muscles shortened during forward sway.
  • Demonstrated that the compliant Achilles tendon decouples muscle contractile changes from body sway.

Conclusions:

  • The compliant Achilles tendon makes the body unstable, requiring active muscle modulation for balance.
  • Stretch reflexes mediated by muscle spindles may not effectively regulate balance due to mechanical decoupling.
  • The primary role of calf muscle spindles might be signaling motor output rather than directly sensing body sway.