Muscle fatigability and post-acute COVID-19 syndrome: A case study, 2022, Fanous et al

Abstract

The acute phase of COVID-19 has been well studied, however with increasing post-acute COVID-19 syndrome, much is unknown about its long-term effects. A common symptom in both the acute and post-acute phases has been fatigue, assessed predominantly qualitatively.

Here we present a case study objectively assessing neuromuscular fatiguability in a young male (27 year, 1.85 m, 78 kg) who continues to experience COVID-19 related fatigue and cognitive dysfunction, including other symptoms, 12+ months post-infection. Prior to infection, he was part of a neuromuscular study forming the basis of our pre-COVID-19 results. The study was repeated 12 months post-COVID-19 infection.

Muscle strength, endurance, torque steadiness, voluntary activation, twitch properties, electromyography, and compound muscle action potential were obtained and compared pre- and post-COVID-19. All measurements were done using a dorsiflexion dynamometer in which the participant also was asked to produce a one-minute fatiguing maximal voluntary contraction. Muscle strength, voluntary activation, and fatigability (slope of torque) showed no meaningful differences, suggesting intrinsic neuromuscular properties are not affected. However, torque steadiness was impaired three-fold in the post- compared with pre-COVID-19 test.

The participant also reported a higher level of perceived exertion subjectively and a continued complaint of fatigue. These findings indicate that muscle fatiguability in post-acute COVID-19 syndrome may not be a limitation of the muscle and its activation, but a perceptual disconnect caused by cognitive impairments relating to physical efforts. This case report suggests the potential value of larger studies designed to assess these features in post-acute COVID-19 syndrome.

Open access: https://physoc.onlinelibrary.wiley.com/doi/10.14814/phy2.15391

 

"Some studies have raised the possibility that COVID-19 may be causing chronic fatigue syndrome (CFS) in post-acute COVID-19 and thus leading to the observed fatigue complications (Deumer et al., 2021; Murga et al., 2021), but in this case, there was no reduction in actual muscle torque nor a decrease in voluntary activation calculated using the twitch interpolated technique (Todd et al., 2004). A decrease in both is a major hallmark for CFS (Sacco et al., 1999).

Additionally, there were no changes in neural drive to the muscles as assessed by similar relative EMG activity, CMAP amplitude, and voluntary activation. Although the sense of effort was greater (not objectively quantified) pain sensitivity subjectively reported was not changed. Agergaard et al. (2021) also noted no significant difference in CMAP parameters in their sample of COVID-19 subjects, but they did report that intramuscular EMG measures were suggestive of myopathic changes. With no change in absolute strength or endurance capacity we have no evidence of any possible myopathic changes, however, it could be one contributing factor to the change in steadiness that requires further investigation.

Indeed, the combination of these measures and observations in this one participant supports that there may be other factors, differing from CFS, causing the reported general sense of activity-dependent fatigue and feeling of weakness. This could indicate that central factors related to cognitive functions (brain fog) or perception have been altered."

 

Their conclusions don't follow from their methodology as no one has shown the "slope of torque" on a 1 minute maximal contraction test to be useful for measuring fatigue even in muscular dystrophies and peripheral neuropathies.

They speculate as to the role of peripheral afferents (which is correct), but they seem to have no clue on the relationship between peripheral fatigue, central fatigue, fatigue-associated sensations and sense of effort (despite all of this stuff being explained in the literature if you dig deep enough).