Skeletal muscle may be a key—yet underappreciated—bridge between long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a new study suggests. Researchers report that muscle characteristics in people with long COVID or ME/CFS are not simply “deconditioning effects” that mirror what happens after bed rest. Instead, the findings point to a different biological signature, potentially reflecting distinct or at least non-identical pathways of impairment.
Using an approach designed to compare conditions rather than treat symptoms in isolation, the team examined skeletal muscle properties across groups and contrasted them with data from bed-rest studies. Bed rest typically produces predictable changes: muscles lose mass, mitochondrial performance can decline, and metabolic flexibility worsens. Those patterns represent the body’s response to reduced loading.
The new work shows that, while long COVID and ME/CFS do involve muscle alterations, the observed features diverge from the specific remodeling seen during disuse. In particular, the muscle phenotypes do not align neatly with the “bed-rest blueprint” researchers often use as a proxy for inactivity-related decline. That mismatch matters because it challenges a common assumption that chronic fatigue syndromes are primarily driven by prolonged low activity alone.
Technically, the study emphasizes comparative muscle biology—analyzing traits tied to muscle structure and function that can include metabolic capacity, fiber-related characteristics, and signaling pathways responsive to physiological stress. By looking for differences against a controlled benchmark of inactivity, the authors identify signatures that appear condition-associated rather than load-associated.
The implications extend beyond classification. If long COVID and ME/CFS share some overlapping muscle mechanisms but still differ from bed-rest physiology, therapies focused purely on reconditioning may be necessary but insufficient. Patients may require interventions that address underlying tissue-level dysregulation, not just activity restoration.
The work also supports the idea that chronic post-viral illness can drive sustained remodeling of muscle physiology through mechanisms distinct from general disuse. That distinction could influence clinical trial design, biomarker development, and how clinicians interpret muscle weakness or endurance limitations in these patients.
For the broader science audience, the most viral takeaway is simple: fatigue in long COVID and ME/CFS may leave a “non-bed-rest” fingerprint in skeletal muscle. That fingerprint could help researchers refine targets—and help patients and healthcare systems stop equating chronic symptoms with mere inactivity.
Subject of Research: Skeletal muscle properties in long COVID and ME/CFS, compared with bed-rest-induced changes.
Article Title: Skeletal muscle properties in long COVID and ME/CFS differ from those induced by bed rest.
Article References: Charlton, B.T., Slaghekke, A., Appelman, B. et al. Nat Commun (2026). https://doi.org/10.1038/s41467-026-75725-y
Image Credits: AI Generated
DOI: 10.1038/s41467-026-75725-y
Keywords: long COVID; ME/CFS; skeletal muscle; bed rest; muscle remodeling; metabolic function; chronic fatigue.
Tags: biological signatures of muscle impairmentcomparative muscle biology in fatigue conditionsdistinct pathways of muscle impairment in chronic fatigueeffects of bed rest on muscle morphologyLong COVID skeletal muscle changesME/CFS muscle propertiesmitochondrial performance in ME/CFSmuscle deconditioning vs. disease-specific alterationsmuscle metabolic flexibility in long COVID and ME/CFSmuscle remodeling in chronic fatigue syndromesmuscle tissue analysis in post-viral syndromesskeletal muscle bioenergetics in long COVID
