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Spreading of fatigue-related effects from active to inactive parts in the medial gastrocnemius muscle of the cat
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Sports Medicine.
Centre for Musculoskeletal Research, National Institute for Working Life - Umeå.
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2002 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 86, no 4, 295-307 p.Article in journal (Refereed) Published
Abstract [en]

In the medial gastrocnemius muscle of the decerebrate cat, the spatial spread of fatigue between active and inactive muscle parts was studied. Conditioning fatiguing stimulation (CFS) was applied to a part of the muscle to test whether it had an effect on the contraction efficiency in an unstimulated part. To exclude somato-sympathetic reflexes during CFS, a full rhizotomy of the lumbo-sacral spinal cord was performed. The same ipsilateral ventral root, either L7 or S1, was divided into seven filaments, one of which was used for the test stimulation, and four or five for CFS. The CFS consisted of 12 s sessions of distributed stimulation of five (or four) filaments at a rate of 40 s(-1), the sessions were repeated, every 40 s, 15 or more times. The test consisted of 12 s of regular stimulation at a rate of 10 s(-1), preceded and followed by a single stimulus. The tests applied just after CFS showed a strong decline of both tension and electromyogram (EMG), amounting to only [mean (SD)] 0.45 (0.18) and 0.51 (0.19) (n = 15), respectively, of the corresponding values in the tests before CFS. It thus turned out that depressive fatigue-related effects could spread within the muscle. At the same time, control reactions recorded in the lateral gastrocnemius during stimulation of its cut nerve did not change. Subsequent repetitions of the tests usually revealed a tendency towards restoration. The EMG reactions recovered more quickly than tension. The depression of EMG after CFS was accompanied by a slowing of the constituent M-waves; their latencies decreased during restoration. Distinct changes in the systemic blood pressure were observed during CFS. These changes were usually correlated well with muscle tension changes. The factors possibly underlying the observed effects may include diffusion of metabolites from active to inactive muscle fibres, lowering of the efficiency of neuro-muscular transmission due to squeezing of efferent motor terminals and changes in outer metabolite content, as well as local hypoxia due to increases in intramuscular pressure.

Place, publisher, year, edition, pages
2002. Vol. 86, no 4, 295-307 p.
Keyword [en]
Muscle fatigue, Electromyography, Blood pressure, Interstitium, Ischaemia
National Category
Medical and Health Sciences
URN: urn:nbn:se:umu:diva-4149DOI: 10.1007/s00421-001-0550-8PubMedID: 11990742OAI: diva2:143131
Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2010-06-28Bibliographically approved
In thesis
1. Experimental studies of spinal mechanisms associated with muscle fatigue
Open this publication in new window or tab >>Experimental studies of spinal mechanisms associated with muscle fatigue
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Muscle fatigue is ubiquitous in every day life.Muscle fatigue might be considered as an altered state of motor behaviour, which impairs motor performance. By contrast, muscle fatigue could also be considered a positive phenomenon, which protects muscle tissue from damage that might be incurred to it by overuse.

The principal aim of the thesis was to explore some of the mechanisms of muscle fatigue at the spinal level in animal models.The activation of multiple motor units of a single calf muscle may influence contractile properties of its neighbouring, otherwise inactive units, providing evidence for spatial spreading of fatigue between different muscle parts. The release of metabolites, their action on inactive muscle units and the effects of local hypoxia are the most likely causes. Fatigue-induced metabolite shift in the interstitium provokes excitation and/or sensitisation of high-threshold afferent fibers, with complex effects on the spinal premotoneuronal network involved in the modulation of motoneuronal output. This was examined by studing the intrasegmental lamellar distribution of the lumbar spinal interneurons following fatiguing contractions of the triceps surae muscle. Furthermore, fatigue of calf muscles enhanced the activity of fusimotor neurons to these muscles irrespective of the regime of muscle activity (isometric vs. lengthening) in conditions that simulate locomotion. Altered fusimotor activity, through increased or maintained muscle spindle afferent responsiveness may be advantageous, providing support to the skeletomotor activity and enhanced information about muscle periphery to higher nervous centres. The particular effects of interneuronal network at motor input (presynaptic inhibition system) and output (recurrent inhibition system) stages were then addressed. Fatigue of triceps surae muscle induced a suppression of the monosynaptic reflex. The intensity of presynaptic inhibition increased, while the intensity of recurrent inhibition decreased. Post fatigue-evoked changes in monosynaptic reflexes and presynaptic inhibition indicate the possibility that high-threshold afferents inhibit group Ia terminals pre-synaptically, which would allow fatigue-induced signals from the muscle to reduce the relevance of proprioceptive feedback. Besides intrasegmental, intersegmental spreading of nociceptive signals was explored. Activation of sensory afferents from dorsal neck muscles by capsaicin induces powerful activation of interneurons located in the cervical spinal cord, as well as a widespread activation of cells in lumbar spinal cord segments.

The results confirm the pivotal role of small diameter muscle afferents in the orchestration of segmental responses to fatigue and show complex interactions that may lead to limited accuracy of motor output. They also depict processes that may be related to, and even become precursors of chronic muscle pain.

Umeå University medical dissertations, ISSN 0346-6612 ; 910
muscle fatigue, monosynaptic reflex, presynaptic inhibition, recurrent inhibition, fusimotor system, Fos-immunoreactivity, referral pain
Research subject
urn:nbn:se:umu:diva-332 (URN)91-7305-703-7 (ISBN)
Public defence
2004-11-12, Stora salen, Arbetslivsinstitutet, 13:00
Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2010-06-28Bibliographically approved

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