Preprint: EEG-Based Spectral Analysis Showing Brainwave Changes Related to Modulating Progressive Fatigue...., 2022, Suviseshamuthu et al

Full title: EEG-Based Spectral Analysis Showing Brainwave Changes Related to Modulating Progressive Fatigue During a Prolonged Intermittent Motor Task

Abstract

Repeatedly performing a submaximal motor task for a prolonged period of time leads to muscle fatigue comprising a central and peripheral component, which demands a gradually increasing effort. However, the brain contribution to the enhancement of effort to cope with progressing fatigue lacks a complete understanding. The intermittent motor tasks (IMTs) closely resemble many activities of daily living (ADL), thus remaining physiologically relevant to study fatigue. The scope of this study is therefore to investigate the EEG-based brain activation patterns in healthy subjects performing IMT until self-perceived exhaustion.

Fourteen participants (median age 51.5 years; age range 26-72 years; 5 males) repeated elbow flexion contractions at 40% maximum voluntary contraction by following visual cues displayed on an oscilloscope screen until subjective exhaustion. Each contraction lasted for approximately 5 s with a 2-s rest between trials. The force, EEG, and surface EMG (from elbow joint muscles) data were simultaneously collected. After preprocessing, we selected a subset of trials at the beginning, middle, and end of the study session representing brain activities germane to mild, moderate, and severe fatigue conditions, respectively, to compare and contrast the changes in the EEG time-frequency (TF) characteristics across the conditions.

The outcome of channel- and source-level TF analyses reveals that the theta, alpha, and beta power spectral densities vary in proportion to fatigue levels in cortical motor areas. We observed a statistically significant change in the band-specific spectral power in relation to the graded fatigue from both the steady- and post-contraction EEG data. The findings would enhance our understanding on the etiology and physiology of voluntary motor-action-related fatigue and provide pointers to counteract the perception of muscle weakness and lack of motor endurance associated with ADL. The study outcome would help rationalize why certain patients experience exacerbated fatigue while carrying out mundane tasks, evaluate how clinical conditions such as neurological disorders and cancer treatment alter neural mechanisms underlying fatigue in future studies, and develop therapeutic strategies for restoring the patients' ability to participate in ADL by mitigating the central and muscle fatigue.

www.biorxiv.org/content/10.1101/2021.09.08.458591v3

 

Further quote:

"Future Perspectives. Past studies have reported the association of fatigue with the following frequency bands in pathological conditions: theta, alpha, or beta band in chronic fatigue syndrome (Siemionow et al., 2004; Flor-Henry et al., 2010) and multiple sclerosis.."

 

Added seconded of these references to the forum: https://www.s4me.info/threads/eeg-s...fatigue-syndrome-2010-flor-henry-et-al.24276/

Link to full article = https://sci-hub.se/10.1016/j.pscychresns.2009.10.007

 

I've stopped giving Sci hub links as they will be problematic for many of our members to access - for example, most, if not all, Internet Service Providers in the UK currently prevent Sci hub links from working. Link to the paywalled article is https://www.sciencedirect.com/science/article/abs/pii/S0925492709002406

 

Some ISPs are making it difficult to access Scihub. I don't know what other work arounds there might be but I use a VPN set to match to the specific Scihub domain. This site gives the current domains: https://sci-hub-links.com/

Actually I've just tried it on TOR - and works find. A bit of faff to swap browsers but TOR is free to download and use. https://www.torproject.org/

 

I would say yes. The strength is that it shows correlates of effort in the brain for a repeated (and constant) force output. This is much more useful for observing real-world fatigue than measuring declines in maximal force output.

Curiously:

Which also suggests measuring the decline in force during a continuous/sustained maximal exertion task may not be as relevant!

Note that they tried to measure 'minimum fatigue', 'moderate fatigue' and 'severe fatigue' and they only measured a clear effect for minimum vs severe. Perhaps that is a result of using healthy participants, rather than ill participants though.

There are experimental difficulties discussed by the authors - non-stationarity of EEG signals (which they tried to control for by monitoring non-motor related areas)

The biggest limitation is:

These limitations would make it more difficult to do what I would like to see experimentally, namely the difference in EEG and EMG responses during submaximal exertion during pre and post 2-Day CPET, and whether blocking the peripheral afferents has any effect. The most obvious hypothesis is that the fatigue associated with PEM is due to central fatigue driven by ongoing stimulation by peripheral afferents.

Lastly, I find the claims of finding "pointers to counteract the perception of muscle weakness and lack of motor endurance associated with ADL" (activities of daily living) to be questionable. They did not explicity state how they think this could be achieved, but are most likely referring to the cited transcranial magnetic stimulation based studies that showed it was possible to inhibit the feedback mechanisms that lead to central fatigue within the brain itself.

While the authors correctly point out that the key component of central fatigue, namely the reduction in excitability of the motor cortex is driven by muscle afferents, they fail to consider why those muscle afferents have such an effect in the first place. But we do know from other experiments where those afferents are blocked - the result is impaired ventilatory responses which leads to greater peripheral fatigue. The lesson is that central and peripheral fatigue are closely coupled!

 

It is always useful to know how a healthy body works but I hope they bear in mind that we do not know exactly where the biological deficits in ME lie. A patient with ME may do exceptionally well with light exercise because our bodies have made adjustments, like adaptations to low level oxygen areas, but then suddenly fall off. It could be read that we are choosing not to try.

It is typical in ME to be able to lift something heavy once, but repeated light tasks soon shut the muscles down to immobility. It would be good to know why that is so but I worry the psychological lens will blur everything.