A simulation study of reflex instability in spasticity: origins of clonus.

@article{Hidler1999ASS,
  title={A simulation study of reflex instability in spasticity: origins of clonus.},
  author={J. Hidler and W. Rymer},
  journal={IEEE transactions on rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society},
  year={1999},
  volume={7 3},
  pages={
          327-40
        }
}
  • J. Hidler, W. Rymer
  • Published 1999
  • Chemistry, Medicine
  • IEEE transactions on rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society
Clonus is defined as an involuntary rhythmic muscle contraction that generally occurs in people who have sustained lesions involving descending motor pathways in the neuraxis, and is usually accompanied by other signs of reflex hyperexcitability such as spasticity. This paper hypothesizes that clonus arises when two conditions occur simultaneously: 1) the reflex pathway contains long delay times (implying innervation of distal limb muscles, exacerbated when these muscles display slow twitch… Expand
tability in spastic subjects : a simulation study and
The influence of motoneuron pool properties on the stability of the stretch reflex at the ankle in subjects with spinal cord injury was tested using a comprehensive model of the reflex pathway. ThisExpand
Effects of motoneuron properties on reflex stability in spastic subjects: a simulation study
  • J. Hidler, W. Rymer
  • Chemistry, Medicine
  • 2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society
  • 2001
TLDR
The hypothesis that unstable oscillatory behavior, such as the oscillations observed in clonus, will occur when the motoneuron excitability increases in a reflex pathway containing long delays is supported. Expand
Clonus: definition, mechanism, treatment.
TLDR
Clonus is involuntary and rhythmic muscle contractions caused by a permanent lesion in descending motor neurons that may be found at the ankle, patella, triceps surae, wrist, jaw, biceps brachii and there is a sufficient period of time for group II afferents and for other spinal mechanisms to be involved in the clonus. Expand
Limit cycle behavior in spasticity: analysis and evaluation
  • J. Hidler, W. Rymer
  • Physics, Computer Science
  • IEEE Transactions on Biomedical Engineering
  • 2000
TLDR
The authors found that delays in the pathway caused the reflex to come on during the shortening phase of movement, so the additional reflex torque required to sustain oscillatory ankle movements was quite small, and the system is robust to small perturbations within the reflex pathway. Expand
Clonus after human spinal cord injury cannot be attributed solely to recurrent muscle-tendon stretch
TLDR
EMG activity during stretch-induced ankle clonus, stepping, and non-weight-bearing standing had similar burst frequency, burst duration, silent period duration, and coactivation among muscles, indicating that clonic EMG patterns occurred over a wide range of kinematic and kinetic conditions, and thus proprioceptive inputs. Expand
Clonus is explained from increased reflex gain and enlarged tissue viscoelasticity.
TLDR
It is concluded that ankle clonus in stroke and SCI is the result of a combination of, and a relation between, a decrease in threshold and an increase in gain of the motor unit pool and a decreases in optimal muscle length. Expand
Clonus in spastic subjects: a stable limit cycle?
  • J. Hidler, W. Rymer
  • Physics, Medicine
  • Proceedings of the 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.00CH37143)
  • 2000
TLDR
The experimental findings in this study suggest that clonus, an involuntary reflex oscillation commonly exhibited in spastic patients, is a stable limit cycle that is mediated by peripheral reflex pathways. Expand
Modulation of soleus stretch reflexes during walking in people with chronic incomplete spinal cord injury
TLDR
Modulation of stretch reflex excitability during spastic gait, investigating soleus stretch reflexes across the entire gait cycle in nine neurologically normal participants and nine participants with spasticity due to chronic incomplete SCI, suggests that H-reflex investigation would not substitute for stretch reflex investigation in individuals after SCI. Expand
Cutaneous inputs from the back abolish locomotor-like activity and reduce spastic-like activity in the adult cat following complete spinal cord injury
TLDR
Pinching the skin of the back effectively abolished rhythmic activity occurring spontaneously or evoked during reflex testing, irrespective of oscillation frequency, consistent with the hypothesis that locomotion and clonus are produced by common central pattern-generators. Expand
The dominant role of the hip in multijoint reflex responses in human spinal cord injury
TLDR
The findings from this suggest that the mutability of reflexes triggered by hip-mediated sensory signals is reduced, which further elucidate the underlying mechanisms associated with hyperexcitable multijoint reflexes to help guide rehabilitation techniques for controlling unwanted muscle activity and for increasing functional gains in human SCI. Expand
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References

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Clonus in man: a rhythmic oscillation maintained by a reflex mechanism.
TLDR
It is demonstrated that clonus duration is contingent upon joint angle and therefore presumably on the amount of stretch placed on the triceps surae muscle group and not on the central spinal generator hypothesis. Expand
Spastic hypertonia: mechanisms and measurement.
  • R. Katz, W. Rymer
  • Medicine
  • Archives of physical medicine and rehabilitation
  • 1989
TLDR
Investigations suggest that spastic hypertonia may be the result of a decrease in stretch reflex threshold without significant increase in reflex gain, as was previously believed. Expand
Limit cycle behavior in spasticity: analysis and evaluation
  • J. Hidler, W. Rymer
  • Physics, Computer Science
  • IEEE Transactions on Biomedical Engineering
  • 2000
TLDR
The authors found that delays in the pathway caused the reflex to come on during the shortening phase of movement, so the additional reflex torque required to sustain oscillatory ankle movements was quite small, and the system is robust to small perturbations within the reflex pathway. Expand
The ankle stretch reflexes in normal and spastic subjects. The response to sinusoidal movement.
TLDR
It is concluded that whereas the gain of a normal stretch reflex may vary considerably, the stretch reflex of the spastic subject is set at one end of the normal range, and with this high gain the stretch Reflex may support spontaneous clonus in both normal and spastic subjects. Expand
Muscle spindle activity in alternating tremor of Parkinsonism and in clonus.
TLDR
The findings are considered to support the notion that, like the contractions in normal voluntary alternating movements, thecontractions in tremor of Parkinsonism are organized according to the principle of alpha-gamma coactivation, whereas the contraction in clonus are stretch reflexes causing pure alpha contractions. Expand
Clonus: the role of central mechanisms.
TLDR
The peripheral and central components in sustained clonus were investigated and it was concluded that the motoneurons responding clonically to a continuous stretch cannot respond until their excitability has been regained after the refractory period. Expand
Antagonistic muscles in the production of clonus in man
TLDR
It has been demonstrated that clonus occurs in a typical fashion even though the antagonists of the clonic muscle had been denervated peripherally by means of electromyography and reversible nerve blocks. Expand
Altered patterns of reflex excitability subsequent to contusion injury of the rat spinal cord.
TLDR
The data indicate that significant changes in lumbar reflex excitability result from midthoracic contusion injury of the spinal cord, including reflex threshold, slope of recruitment, and rate-sensitive depression. Expand
Quantitative relations between hypertonia and stretch reflex threshold in spastic hemiparesis
TLDR
The relative contributions of variations in stretch reflex threshold and total joint stiffness to changes in stretch‐evoked torque were assessed in the spastic elbow muscles of 14 hemiparetic spastic subjects, suggesting that reductions in stretch Reflex threshold are uniformly present in spastic muscles. Expand
Clonus: beats provoked by the application of a rhythmic force.
  • E. Walsh
  • Medicine
  • Journal of neurology, neurosurgery, and psychiatry
  • 1976
TLDR
It is concluded that clonus is not due to the self re-excitation of proprioceptive reflexes but is dependent on a spinal generator, the rate of beating of which is normally independent of peripheral circumstances, although it may be switched on and its activity maintained by appropriate events. Expand
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