Reports describe the frequent occurrence of Skeletal muscle‐related symptoms in both acute coronavirus disease (Covid‐19 and post‐acute sequelae of Covid‐19 (PASC). A recent narrative review discussed cellular and molecular pathways that are affected and considered these with skeletal muscle involvement in other conditions, such as acute respiratory distress syndrome, critical illness myopathy, and post‐viral fatigue syndrome. 

Patients with severe Covid‐19 and PASC experience skeletal muscle weakness and exercise intolerance. Histological study shows muscle fiber atrophy, metabolic alterations, and immune cell infiltration. Factors such as systemic inflammation, disuse, hypoxemia, and malnutrition may further increase weakness and fatigue in patients with severe Covid‐19. Furthermore, these factors also contribute to post‐intensive care unit (ICU) syndrome and ICU‐acquired weakness and probably explain a significant part of Covid‐19‐acquired weakness. 

The skeletal muscle weakness and exercise intolerance associated with PASC are more mysterious. Direct severe acute respiratory syndrome coronavirus (SARS‐CoV)‐2 viral infiltration into skeletal muscle or an impaired immune system possibly contribute to its development.

It would be useful to investigate the similarities between PASC and chronic fatigue syndrome regarding skeletal muscle alterations. Along with the specific factors, generic consequences of acute disease are likely to influence the skeletal muscle alterations identified in acute Covid‐19 and PASC. There is a need for tailored interventions based on a more in‐depth, fundamental understanding of skeletal muscle alterations and the underlying determinants to attenuate clinical symptoms and improve quality of life in patients with acute Covid‐19 and PASC.

Soares MN, Eggelbusch M, Naddaf E, Gerrits KHL, van der Schaaf M, van den Borst B, Wiersinga WJ, van Vugt M, Weijs PJM, Murray AJ, Wüst RCI. Skeletal muscle alterations in patients with acute Covid-19 and post-acute sequelae of Covid-19. J Cachexia Sarcopenia Muscle. 2022 Feb;13(1):11-22. doi: 10.1002/jcsm.12896. Epub 2022 Jan 7. PMID: 34997689; PMCID: PMC8818659.