Opinion Editorial: Fatigue: Physiology and Pathology, 2024, Kujawski/Zalewski/Hodges/Nijs/Newton

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https://www.frontiersin.org/articles/10.3389/fnins.2024.1368897/full

EDITORIAL article
Front. Neurosci.
Sec. Autonomic Neuroscience
Volume 18 - 2024 | doi: 10.3389/fnins.2024.1368897

Editorial: Fatigue: Physiology and Pathology
This article is part of the Research Topic
Fatigue: Physiology and Pathology

View all 10 Articles
Sławomir Kujawski1* Paweł Zalewski2, 3 Lynette Hodges4 Jo Nijs5, 6, 7 Julia L. Newton8

• 1Department of Exercise Physiology and Functional Anatomy, Ludwik Rydygier Collegium Medicum in Bydgoszcz Nicolaus Copernicus University in Toruń, Bydgoszcz, Poland, Poland
• 2Department of Exercise Physiology and Functional Anatomy, Faculty of Health Sciences, Nicolaus Copernicus University in Toruń, Poland
• 3Department of Experimental and Clinical Physiology, Medical University of Warsaw, Poland
• 4School of Sport, Exercise and Nutrition, College of Health, Massey University, New Zealand
• 5Faculty of Physical Education and Physiotherapy, Vrije Universiteit Brussel, Belgium
• 6Chronic Pain Rehabilitation, Department of Physical Medicine and Physiotherapy, University Hospital Brussels, Belgium
• 7Department of Neuroscience and Physiology, University of Gothenburg, Sweden
• 8Population Health Sciences Institute, Faculty of Medical Sciences, Newcastle University, United Kingdom

 

Really just introduces the 10 papers published during 2023 as part of the Research Topic 'fatigue' Includes ME and non-ME fatigue), so nothing new. Except for the introduction which is, um, different

 

Some interesting use of language in this section as well. "PEM is a crucial source of suffering in the majority of ME/CFS patients" isn't how I would have chosen to describe it. My guess is that they are trying to say that PEM is a core symptom?

"Fatigue pathology: MS, ME/CFS, Long COVID

1.4. It should be noted that in some circumstances, acute fatigue seems to be a physiological response to a higher workload. In healthy people, fatigue can be alleviated by rest in a rather short matter of time. However, in patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), an increase in symptom severity can be caused by relatively low intensity physical, emotional, or psychological stressors. Post-exertional malaise (PEM) is a crucial source of suffering in the majority of ME/CFS patients. PEM is comprehensively described in the paper by Vøllestad and Mengshoel (Vøllestad and Mengshoel). [Discussion thread for this paper here]

1.5. Core symptoms of ME/CFS also often occur in long COVID (otherwise known as post-acute sequelae of COVID-19) patients, and may include fatigue, pain, post-exertional malaise, breathing difficulties, and cognitive dysfunction (Davis et al., 2021, Komaroff and Bateman, 2021). In the current main paradigm of science, it is assumed that symptoms perceived by patients are output products of the nervous system. However, there is still much to explore and the study of Thapaliya et al. seems to be a very important step in this direction (Thapaliya et al.). “Pain” and “breathing difficulty” perceived by patients were related to multiple brain regions, including pons, midbrain, and whole brainstem volumes (Thapaliya et al.).

1.6. The last decades of research in human neuroscience have produced an appreciation of bidirectional cooperation between the nervous system and its effectors. In this line, Day et al. have provided a study on the relationship between changes in the cardiovascular system response to changing position from prone to supine with cognitive dysfunction in patients suffering from ME/CFS and long COVID (Day et al.).

1.7. Fatigue is a non-specific symptom, occurring in multiple chronic disorders. In addition, to the description of fatigue in Multiple Sclerosis (MS), Pinarello et al. described modes of treatment of MS both pharmacological and non-pharmacological including telemedicine approach (Pinarello et al.)."

 

This is a great topic (I haven't read any of the papers yet). The physiology of pathological fatigue in general isn't well understood (it's not sorted for healthy fatigue either). Presumably, progress in these areas would help the understanding of MEcfs.

1.8. In skeletal muscle physiology, peripheral fatigue refers to a group of changes occurring in response to prolonged muscle activity, while central fatigue is the inability of the nervous system to produce and transmit the signal to contract to the effectors (Dotan et al., 2023). This distinction is somewhat controversial, as there seems to be no clear barrier between “peripheral” vs. “central” (Dotan et al., 2023).
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Can anyone help with Dotan 2023? The distinction between central and peripheral fatigue was supposed to be one of the understood areas.

 

It seems to be this paper, which seems to be a rather obscure study comparing boys and men for 'Mean Power Frequency'.

Eur. J Applied Physiol. . 2023 Aug 9.
doi: 10.1007/s00421-023-05292-3. Online ahead of print.
Boys-men mean-power-frequency differences in progressive exercise to exhaustion, confounded by variability and adiposity
Raffy Dotan 1, Stacey Woods 2, Jordan Langille 2, Bareket Falk 2
PMID: 37553549
DOI: 10.1007/s00421-023-05292-3
Abstract
Background: Only scant research has compared children's mean power frequency (MPF) to adults', with a clear overview still lacking. A significant obstacle has been MPF's high variability, which this study aimed to overcome by elucidating the MPF characteristics distinguishing boys from men in progressive exhaustive exercise.
Methods: Electromyographic (EMG) data of 20 men (23.5 ± 2.5yrs) and 17 boys (10.2 ± 1.0 yrs), who performed progressively exhausting, intermittent isometric knee extensions, were subjected to secondary MPF analysis. Participants' vastus lateralis MPF data series were transformed to third-order polynomial regressions and expressed as percentages of the peak polynomial MPF values (%MPFpeak). The resulting curves were compared at 5-% time-to-exhaustion (TTE) intervals, using repeated-measures ANOVA. Raw MPFpeak values were adiposity corrected to 0% fat and used to convert the %MPFpeak data back to absolute MPF values (Hz) for estimating muscle-level MPF.

Results: No overall interaction or group effects could be shown between the %MPFpeak plots, but pairwise comparisons revealed significantly higher men's values at 50-70%TTE and lower at 100%TTE, i.e. boys' shallower MPF rise and decline. The adiposity-corrected boys' and men's composite MPF values peaked at 125.7 ± 2.5 and 166.0 ± 2.4 Hz, respectively (110.7 ± 1.7 and 122.5 ± 2.1 Hz, uncorrected), with a significant group effect (p < 0.05) and pairwise differences at all %TTE points.

Conclusions: The boys were lower than the men in both the observed and, more so, in the adiposity-corrected MPF values that presumably estimate muscle-level MPF. The boys' shallower MPF rise and decline conform to children's claimed type-II motor-unit activation and/or compositional deficits and their related known advantage in muscular endurance.

 

Thanks. I struggle to see in such a small study how these findings undermines the idea of a distinction between peripheral and central fatigue.

 

I agree. Also, I suppose that the relation in healthy people is a different matter from the relation between one in one disease and the other in another disease.

 

For what it is worth, the full version of the editorial is now available, and the paper they actual reference from Dotan et al is this one,

On the reliability and validity of central fatigue determination, 2021, Dotan et al

Abstract

Physical performance fatigue can be ascribed to both peripheral and central components. Central fatigue, however, is an elusive entity, consisting of cognitive/sensory component and presumably also a neuro-physiological component that are difficult to tease apart and assess independently of each other. The most widely accepted method for the assessment of central fatigue is based on the premise that decreasing volitional muscle activation (VA), as determined by the interpolated twitch technique (ITT) in fatiguing muscles, reflects increasing central fatigue. Suffering its own shortcomings, the validity of VA determination under fatigued conditions has never been proven and is only assumed. This review presents evidence that questions ITT’s reliability and validity in reflecting VA in the fatiguing muscle and, consequently, VA’s validity for central fatigue assessment. Specifically highlighted is the paradox of children and endurance athletes, who share striking endurance characteristics, being claimed as more centrally fatigable than untrained adults. Further research and new directions are needed for confirming and quantifying central fatigue and teasing apart its psychologic and neuromotor components.

Paywall, https://link.springer.com/article/10.1007/s00421-021-04700-w