Muscle and brain fatigue

[Guest guest]

Fatigue-induced increase in intracortical communication between mid/anterior

insular and motor cortex during cycling exercise

Lea Hilty1,2,3, Nicolas Langer3, o Pascual-Marqui4,5, Urs Boutellier1,2,

Kai Lutz3Article first published online: 20 NOV 2011

DOI: 10.1111/j.1460-9568.2011.07909.x

Keywords:EEG;exercise;homeostatic functions;lagged phase

synchronization;supraspinal fatigue

Abstract

In the present study, intracortical communication between mid/anterior insular

and motor cortex was investigated during a fatiguing cycling exercise. From 16

healthy male subjects performing a constant-load test at 60% peak oxygen

consumption (VO2peak) until volitional exhaustion, electroencephalography data

were analysed during repetitive, artefact-free periods of 1-min duration. To

quantify fatigue-induced intracortical communication, mean intra-hemispheric

lagged phase synchronization between mid/anterior insular and motor cortex was

calculated: (i) at the beginning of cycling; (ii) at the end of cycling; and

(iii) during recovery cycling. Results revealed significantly increased lagged

phase synchronization at the end of cycling, which returned to baseline during

recovery cycling after subjects' cessation of exercise.

Following previous imaging studies reporting the mid/anterior insular cortex as

an essential instance processing a variety of sensory stimuli and signalling

forthcoming physiological threat, our results provide further evidence that

during a fatiguing exercise this structure might not only integrate and evaluate

sensory information from the periphery, but also act in communication with the

motor cortex. To the best of our knowledge, this is the first study to

empirically demonstrate that muscle fatigue leads to changes in interaction

between structures of a brain's neural network.

==============

Carruthers

Wakefield, UK

[Guest guest]

Relevant to the below:

http://medicalxpress.com/news/2011-12-muscle-fatigue.html

The extent to which we are able to activate our muscles voluntarily depends on

motivation and will power or the physical condition and level of fatigue of the

muscles, for instance. The latter particularly leads to noticeable and

measurable performance impairments. For a long time, the research on muscle

fatigue was largely confined to changes in the muscle itself.

Now, a joint research project between the University of Zurich and ETH Zurich

has shifted the focus to brain research. Headed by neuro-psychologist Kai Lutz

from the University of Zurich in collaboration with Urs Boutellier from the

Institute of Human Movement Sciences and Sport at ETH Zurich, the researchers

discovered neuronal processes for the first time that are responsible for

reducing muscle activity during muscle-fatiguing exercise. The third and final

part of this series of experiments, which was conducted by Lea Hilty as part of

her doctoral thesis, has now been published in the European Journal of

Neuroscience.

Muscle's nerve impulses inhibit motoric area in the brain

In the initial study, the researchers showed that nerve impulses from the muscle

– much like pain information – inhibit the primary motoric area during a tiring,

energy-demanding exercise. They were able to prove this using measurements in

which study participants repeated thigh contractions until they could no longer

attain the force required. If the same exercise was conducted under

narcotization of the spinal chord (spinal anesthesia), thus interrupting the

response from the muscle to the primary motoric area, the corresponding

fatigue-related inhibition processes became significantly weaker than when the

muscle information was intact.

In a second step, using functional magnetic resonance imaging, the researchers

were able to localize the brain regions that exhibit an increase in activity

shortly before the interruption of a tiring, energy-demanding activity and are

thus involved in signalizing the interruption: the thalamus and the insular

cortex – both areas which analyze information that indicates a threat to the

organism, such as pain or hunger.

Neuronal system has regulating effect on muscle performance

The third study has now shown that the inhibitory influences on motoric activity

are actually mediated via the insular cortex: In tests using a bicycle

ergometer, the researchers determined that the communication between the insular

cortex and the primary motoric area became more intensive as the fatigue

progressed. " This can be regarded as evidence that the neuronal system found not

only informs the brain, but also actually has a regulating effect on motoric

activity, " says Lea Hilty, summing up the current result. And Kai Lutz points to

the new research field that now opens up with these results: " The findings are

an important step in discovering the role the brain plays in muscle fatigue.

Based on these studies, it won't just be possible to develop strategies to

optimize muscular performance, but also specifically investigate reasons for

reduced muscular performance in various diseases. " Prolonged reduced physical

performance is a symptom that is frequently observed in daily clinical practice.

It can also appear as a side effect of certain medication. However, so-called

chronic fatigue syndrome is often diagnosed without any apparent cause.

>

> Fatigue-induced increase in intracortical communication between mid/anterior

insular and motor cortex during cycling exercise

> Lea Hilty1,2,3, Nicolas Langer3, o Pascual-Marqui4,5, Urs Boutellier1,2,

Kai Lutz3Article first published online: 20 NOV 2011

>

> DOI: 10.1111/j.1460-9568.2011.07909.x

>

> Keywords:EEG;exercise;homeostatic functions;lagged phase

synchronization;supraspinal fatigue

> Abstract

> In the present study, intracortical communication between mid/anterior insular

and motor cortex was investigated during a fatiguing cycling exercise. From 16

healthy male subjects performing a constant-load test at 60% peak oxygen

consumption (VO2peak) until volitional exhaustion, electroencephalography data

were analysed during repetitive, artefact-free periods of 1-min duration. To

quantify fatigue-induced intracortical communication, mean intra-hemispheric

lagged phase synchronization between mid/anterior insular and motor cortex was

calculated: (i) at the beginning of cycling; (ii) at the end of cycling; and

(iii) during recovery cycling. Results revealed significantly increased lagged

phase synchronization at the end of cycling, which returned to baseline during

recovery cycling after subjects' cessation of exercise.

>

> Following previous imaging studies reporting the mid/anterior insular cortex

as an essential instance processing a variety of sensory stimuli and signalling

forthcoming physiological threat, our results provide further evidence that

during a fatiguing exercise this structure might not only integrate and evaluate

sensory information from the periphery, but also act in communication with the

motor cortex. To the best of our knowledge, this is the first study to

empirically demonstrate that muscle fatigue leads to changes in interaction

between structures of a brain's neural network.

>

==============

Carruthers

Wakefield, UK