Jitter and muscle fiber conduction velocity in long COVID fatigue

Sep 29, 2026

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Background describes long coronavirus disease (long COVID, LC) as the continuation or development of new symptoms at least 3 months after acute SARS-CoV-2 infection. Fatigue or post-exertional malaise (F-PEM) occurs in up to 70% of cases and is common across ages and acute severities. Objective: evaluate neuromuscular junction function and isolated muscle fiber conduction velocity (MFCV) in LC cases and controls. Methods compared 37 controls and 32 infected participants using single-fiber electromyography jitter, MFCV, F/S ratio, and motor unit potentials; results found LC-yes differed mainly by F-PEM without electrophysiological evidence implicating NMJ or muscle fiber function as a key factor.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages8

Reading Time20 min

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Background

Objective

Methods

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Article published online: 2025-02-24 Original Article 1 Jitter and muscle ﬁber conduction velocity in long COVID fatigue João Aris Kouyoumdjian 1 Leticia Akemi Rama Yamamoto 1 Carla Renata Graca 1 1 Faculdade Estadual de Medicina de São José do Rio Preto (FAMERP), Departamento de Ciências Neurológicas, Psiquiatria e Psicologia Médica, Laboratório de Investigação Neuromuscular, São José do Rio Preto SP, Brazil. Arq. Neuro-Psiquiatr. 2025;83(1):s00451802961 . Address for correspondence João Aris Kouyoumdjian (email: [jaris@famerp.br](jaris@famerp.br)). Abstract Keywords ► SARS-CoV-2 ► Post-Acute COVID-19 Syndrome ► Fatigue ► Single-Fiber Electromyography ► Muscle Fiber Conduction Velocity Background Long coronavirus disease (long COVID, LC) is deﬁned as the continuation or development of new symptoms 3 months after the acute stage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In LC, the rate of fatigue/postexertional malaise (F-PEM) has been described to be as high as 70%, regardless of age or severity of the acute symptoms. Objective To evaluate the neuromuscular junction (NMJ) function and the isolated muscle ﬁber conduction velocity (MFCV) in situ in LC cases and controls. Methods We studied 37 subjects without SARS-CoV-2 (controls) and 32 cases of SARS-CoV-2 infection, half with LC symptoms (LC-yes) and half without them (LC-no) . Single-ﬁber electromyography (jitter measured with a concentric electrode), MFCV, the fast-to-slow MFCV ratio (F/S ratio), and the motor unit potentials (MUPs) were taken in the tibialis anterior muscle. Results At least 1 jitter parameter was abnormal in 1/37 controls, in 1/16 LC-no patients, and in 2/16 LC-yes patients, without signiﬁcant differences among them. None of the subjects with abnormal jitter presented ﬂuctuation symptoms or positive acetylcholine-receptor antibody. The MFCVand F/S ratios did not show abnormalities in any of the participants. The MUPs did not show myopathic or neurogenic abnormality in needle electromyography. The most frequent symptom in LC was F-PEM, which occurred in all LC-yes patients and was signiﬁcantly different from the other groups. Conclusion Fatigue/postexertional malaise was found in all cases of LC, and the electrophysiological ﬁndings did not indicate the muscle ﬁber or the NMJ as a relevant factor in this condition. INTRODUCTION In December 2019, unusual cases of pneumonia were reported in China, which quickly spread to other parts of the country and then worldwide. This outbreak was conﬁrmed to be caused by a novel coronavirus (CoV) .1 The symptomatology was similar to that of severe acute respira- received August 29, 2024 received in its ﬁnal form October 7, 2024 accepted October 13, 2024 DOI [https://doi.org/](https://doi.org/)[ ](https://doi.org/)10.1055/s-0045-1802961 . ISSN 0004-282X. Editor-in-Chief: Hélio A. G. Teive. Associate Editor: Carlos Otto Heise. tory syndrome coronavirus 1 (SARS-CoV-1) in 2003; thus, the virus was termed SARS-CoV-2 . Since then, the World Health Organization (WHO) has counted 775,583,309 cases, with 7,050,691 deaths.2 These numbers are likely much higher due to many undocumented cases.3 The WHO deﬁnes long coronavirus disease(long COVID, LC) as the continuation or development, without explanation, of © 2025 . The Author(s) . This is an open access article published by Thieme under the terms of the Creative Commons Attribution 4.0 International License, permitting copying and reproduction so long as the original work is given appropriate credit ([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)). Thieme Revinter Publicações Ltda. , Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil 2 Jitter and muscle fiber conduction velocity in long COVID Kouyoumdjian et al. new symptoms 3 months after the initial SARS-CoV-2 infection.4,5 Long COVID can manifest in appro

FAQs

What question does this study address about long COVID fatigue?

It evaluates whether neuromuscular junction function and isolated muscle fiber conduction velocity are abnormal in long COVID fatigue cases compared with controls.

How were participants grouped in the study?

There were 37 SARS-CoV-2-negative controls and 32 SARS-CoV-2-infected participants split into LC-yes (half with LC symptoms) and LC-no (half without LC symptoms).

What did the electrophysiological tests show?

Jitter abnormalities were rare and showed no significant group differences, while MFCV and F/S ratios were not abnormal in any participants; motor unit potentials did not show myopathic or neurogenic abnormalities.

Sep 29, 2026

Uploaded by Logic