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Signs of muscle thixotropy during human ballistic wrist joint movements
Uppsala University, Medicinska vetenskapsområdet, Faculty of Medicine, Department of Neuroscience, Clinical Neurophysiology.
Article in journal (Refereed) Submitted
URN: urn:nbn:se:uu:diva-93035OAI: oai:DiVA.org:uu-93035DiVA: diva2:166389
Available from: 2005-05-09 Created: 2005-05-09Bibliographically approved
In thesis
1. Muscle Thixotropy: Implications for Human Motor Control
Open this publication in new window or tab >>Muscle Thixotropy: Implications for Human Motor Control
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human skeletal muscles possess thixotropic, i.e. history-dependent mechanical properties. This means that the degree of passive muscle stiffness and resting tension is dependent on the immediately preceding history of contractions and length changes. Athletes, for instance, reduce passive muscle stiffness by various types of ‘limbering-up’ procedures, whereas muscle stiffness gradually increases during inactivity.

Passive resistance of antagonistic muscles may significantly add to the total load during voluntary muscle contractions. This resistance may vary from one moment to another, depending on immediately preceding events. This research was conducted to determine whether history-dependent variations in passive muscular forces influence motor control of voluntary joint movements and steady maintenance of joint positions in healthy subjects.

In study I, the EMG signal revealed motor compensations for history-dependent variations in passive stiffness of the antagonists during slow voluntary wrist joint movements. Studies II and III demonstrated that the voluntary muscle activity required to maintain a certain wrist joint position was highly influenced by previous changes in forearm muscle length and contractions. Study IV showed that rapid voluntary movements varied in speed and onset time depending on the prevailing degree of muscle resistance, and in addition that the central nervous reaction time required to execute rapid movements was highly influenced by immediately preceding muscle-conditioning procedures.

History-dependent variations in passive muscular forces seem to be effectively compensated by the motor control system. Presumably, voluntary motor commands to the muscles are automatically adjusted in strength to history-dependent changes in passive muscular forces. Such adjustments occur within the central nervous system, which receives information about the mechanical state of the muscles. Several issues in connection with muscle thixotropy remain unaddressed. For instance, do alterations in the normal thixotropic mechanical behaviour of the muscles impose a particular problem in patients with certain neuromuscular diseases?

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. 56 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 38
Neurosciences, Motor control, Skeletal muscle, Thixotropy, History-dependent, EMG, Voluntary contractions, Neurovetenskap
National Category
urn:nbn:se:uu:diva-5791 (URN)91-554-6246-4 (ISBN)
Public defence
2005-05-28, Rudbecksalen, Rudbecklaboratoriet, Uppsala, 13:15
Available from: 2005-05-09 Created: 2005-05-09Bibliographically approved

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