Charlton 2026 Muscle-Bedrest Stream

1 Charlton et al. 2026 — Skeletal Muscle Properties in Long COVID and ME/CFS Differ from Those Induced by Bed Rest

  • Full Citation:: Charlton BT, Slaghekke A, Appelman B, Eggelbusch M, Huijts JY, Noort W, Hendrickse PW, Bloemers FW, Posthuma JJ, van Amstel P, Goulding RP, Degens H, Jaspers RT, van Vugt M, Wüst RCI. Skeletal Muscle Properties in Long COVID and ME/CFS Differ from Those Induced by Bed Rest. Nature Communications. 2026. Article in Press. (Charlton et al. 2026)
  • DOI:: 10.1038/s41467-026-75725-y
  • Study Design:: Cross-sectional comparison: strict 60d head-down tilt bed rest (n=24 healthy, longitudinal pre-post) vs long COVID (n~25), ME/CFS (n~26, pre-2020 dx), age/sex-matched healthy controls (n=30)
  • Key Findings::
    • VO2max similarly reduced in patient groups and post-bed rest — but via different physiological mechanisms
    • Bed rest: reduced VEmax, increased VE/VCO2 slope; patients: increased HR-VO2 slope (suggestive of impaired O2 extraction or stroke volume)
    • Bed rest: global muscle atrophy without fiber type change
    • Both patient groups: more glycolytic (type IIa/IIx) fibers (+ decreased type I) — fiber type shift not seen in bed rest
    • ME/CFS: selective type I fiber atrophy — unique to ME/CFS, not in bed rest or long COVID
    • OXPHOS capacity + SDH activity correlated with VO2max in healthy controls and pre/post bed rest (r=0.53–0.74) — this correlation ABSENT in both patient groups (r=0.27–0.31, p>0.14)
    • Bed rest: increased capillary density (atrophy outpaces capillary loss); ME/CFS: lower capillary-to-fiber ratio and density
    • Both patient groups: downshifted capillary-to-fiber vs FCSA relationship (fewer capillaries for given fiber size)
    • Intrinsic mitochondrial dysfunction: lower OXPHOS/SDH ratio, trending lower E/L coupling efficiency in patients (not in bed rest)
    • Myoglobin content similar across groups — suggests maintained intramyocyte O2 diffusion capacity
  • Conclusion:: Physical inactivity/deconditioning alone cannot explain skeletal muscle alterations in long COVID and ME/CFS. Patients show disease-intrinsic mitochondrial dysfunction, fibre type shift, and capillarization deficits that distinguish them from bed rest. Rehabilitation strategies should treat patients as unique cases, not simply deconditioned.
  • Limitations:: Cross-sectional in patients (no pre-disease biopsies); self-selection bias toward milder patients; bed rest cohort younger (30 vs 42 years mean); head-down tilt ≠ ambulatory deconditioning; cannot distinguish disease duration from disease pathophysiology; no sex-specific analysis due to bed rest female underpowering (8/24).
  • Certainty:: 0.85

2 Hendrickse et al. 2022 — Capillary Rarefaction During Bed Rest Is Proportionally Less than Fibre Atrophy and Loss of Oxidative Capacity

  • Full Citation:: Hendrickse PW, Wüst RCI, Ganse B, Giakoumaki I, Rittweger J, Bosutti A, Degens H. Capillary Rarefaction During Bed Rest Is Proportionally Less than Fibre Atrophy and Loss of Oxidative Capacity. Journal of Cachexia, Sarcopenia and Muscle. 2022;13(6):2712-2723. (Hendrickse et al. 2022)
  • DOI:: 10.1002/jcsm.13072
  • PMID:: 36102002
  • Study Design:: Longitudinal: vastus lateralis + soleus biopsies at baseline, 6d, and 55d bed rest (AGBRESA study); n=19
  • Key Findings::
    • Rapid early fibre atrophy (-23% at 6d) with proportional capillary loss (C:F ratio declined)
    • Slower later atrophy (-12% from 6d to 55d)
    • By 55d: capillary supply in relative excess of oxidative capacity (+42%) — uncoupled from mitochondrial loss
    • SDH optical density decreased -19% at 55d without further capillary loss
    • Artificial gravity (30min/d centrifugation) failed to prevent these changes
  • Conclusion:: Prolonged bed rest uncouples capillary supply from oxidative capacity. This creates a capillary-excess state advantageous for recovery — the opposite of what Charlton 2026 finds in ME/CFS (capillary deficit). Foundational bed rest comparator for the primary paper.
  • Limitations:: Small sample (n=19); all healthy volunteers; centrifugation group merged with control for main analysis.
  • Certainty:: 0.75

3 Eggelbusch et al. 2024 — The Impact of Bed Rest on Human Skeletal Muscle Metabolism

  • Full Citation:: Eggelbusch M, Charlton BT, Bosutti A, Ganse B, Giakoumaki I, Grootemaat AE, Hendrickse PW, Jaspers Y, Kemp S, Kerkhoff TJ, Noort W, van Weeghel M, van der Wel NN, Wesseling JR, Frings-Meuthen P, Rittweger J, Mulder ER, Jaspers RT, Degens H, Wüst RCI. The Impact of Bed Rest on Human Skeletal Muscle Metabolism. Cell Reports Medicine. 2024;5(1):101372. (Eggelbusch et al. 2024)
  • DOI:: 10.1016/j.xcrm.2023.101372
  • PMID:: 38232697
  • Study Design:: Same AGBRESA 60d bed rest cohort; multi-omics integrative analysis (metabolomics, lipidomics, EM, respirometry, immunohistochemistry)
  • Key Findings::
    • Short-term (6d): intracellular glycogen accumulation, reduced GLUT4 membrane localization, rapid insulin sensitivity loss
    • Long-term (55d): intramyocellular lipid + ceramide + sphingomyelin accumulation
    • Fragmented mitochondria on EM after 55d
    • Reduced OXPHOS capacity
    • Identified intracellular nutrient overload as determinant of insulin resistance and mitochondrial dysfunction
    • Temporal dissociation: carbohydrate defect (early) vs lipid defect (late)
  • Conclusion:: Bed rest induces a specific metabolic signature (glycogen→lipid overload→mitochondrial fragmentation) that is distinct from the patient phenotype in Charlton 2026 (intrinsic mitochondrial dysfunction without nutrient overload). Supports the conclusion that the metabolic defects in patients are disease-intrinsic.
  • Limitations:: Same cohort size (n=24); head-down tilt model limitations for generalization to clinical deconditioning.
  • Certainty:: 0.80

4 Joseph et al. 2021 — Invasive CPET in ME/CFS: Insights into Exercise Intolerance

  • Full Citation:: Joseph P, Arevalo C, Oliveira RKF, Faria-Urbina M, Waxman AB, Systrom DM. Insights From Invasive Cardiopulmonary Exercise Testing of Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Chest. 2021;160(2):642-651. (Joseph et al. 2021)
  • DOI:: 10.1016/j.chest.2021.01.082
  • PMID:: 33577778
  • Study Design:: Cross-sectional; invasive CPET with radial + pulmonary artery catheters; n=20 ME/CFS (Fukuda 1994) vs n=10 healthy controls
  • Key Findings::
    • Marked reduction in peak systemic O2 extraction (cardiac output × arteriovenous O2 difference) in ME/CFS
    • Reduced stroke volume augmentation with exercise
    • Low biventricular filling pressures — preload failure, not cardiac dysfunction
    • Normal pulmonary gas exchange and pulmonary vascular function
    • Arterial PO2 similar to controls at peak exercise
  • Conclusion:: ME/CFS exercise limitation is primarily peripheral (oxygen extraction + preload failure), not central (lung/heart). Directly supports Charlton 2026’s argument that patient limitations differ from deconditioning — cited as ref 40 in the primary paper.
  • Limitations:: Modest sample; Fukuda criteria (broader phenotype than CCC); single center; no concurrent muscle biopsy.
  • Certainty:: 0.75

5 Singh et al. 2022 — Persistent Exertional Intolerance After COVID-19: Invasive CPET

  • Full Citation:: Singh I, Joseph P, Heerdt PM, Cullinan M, Lutchmansingh DD, Gulati M, Possick JD, Systrom DM. Persistent Exertional Intolerance After COVID-19: Insights From Invasive Cardiopulmonary Exercise Testing. Chest. 2022;161(1):54-63. (Singh et al. 2022)
  • DOI:: 10.1016/j.chest.2021.08.010
  • PMID:: 34389297
  • Study Design:: Cross-sectional; invasive CPET; n=10 post-COVID patients (9 never hospitalized) with unexplained dyspnea/exercise intolerance
  • Key Findings::
    • Peak VO2: 71% predicted — moderate impairment
    • Key finding: reduced peak systemic O2 extraction despite normal cardiac output
    • Some patients showed preload failure (low filling pressures)
    • Normal pulmonary gas exchange ruling out lung parenchymal limitation
  • Conclusion:: Peripherally-mediated exercise limitation (impaired O2 extraction) after COVID-19, consistent with Joseph 2021 in ME/CFS and cited as ref 41 in Charlton 2026.
  • Limitations:: Small sample (n=10); heterogeneous group; no concurrent muscle biopsy.
  • Certainty:: 0.70

6 Germain et al. 2025 — Plasma Proteomics of Post-Exertional Malaise

  • Full Citation:: Germain A, Glass KA, Eckert MA, Giloteaux L, Hanson MR. Temporal Dynamics of the Plasma Proteomic Landscape Reveals Maladaptation in ME/CFS Following Exertion. Molecular & Cellular Proteomics. 2025;24(12):101467. (Germain et al. 2025)
  • DOI:: 10.1016/j.mcpro.2025.101467
  • PMID:: 41237904
  • Study Design:: Longitudinal plasma proteomics (SomaScan 7K, 6361 proteins); n=79 ME/CFS vs n=53 age/BMI-matched sedentary controls; 2-day CPET with samples at 5 timepoints
  • Key Findings::
    • ME/CFS showed persistent immune/metabolic/neuromuscular pathway dysregulation during recovery (PEM onset)
    • Upregulated glycolysis/gluconeogenesis — suggestive of mitochondrial stress
    • Suppressed T/B cell signaling, downregulated IL-17 and cell-cell communication pathways
    • Proteomic associations with VO2max + anaerobic threshold were disrupted in ME/CFS vs controls
    • Sex-stratified: distinct female vs male molecular responses to exertion
    • Sedentary control cohort provides new reference data on molecular responses to acute exertion in females
  • Conclusion:: PEM is accompanied by a specific proteomic signature that is not explained by physical deconditioning. The disrupted proteome-performance associations corroborate Charlton 2026’s finding that OXPHOS-VO2max correlation is lost in patients.
  • Limitations:: Plasma proteomics (not tissue-level); 79 ME/CFS is substantial but heterogenous; no invasive hemodynamics.
  • Certainty:: 0.70

7 Toriola et al. 2026 — ATG13-Dependent Autophagy and Muscle Mitochondrial Function

  • Full Citation:: Toriola MA, Timlin E, Bulbule S, Reyes A, Adedeji OM, Gottschalk CG, Barua A, Arnold LA, Roy A. Genetic Depletion of the Early Autophagy Protein ATG13 Impairs Mitochondrial Energy Metabolism, Augments Oxidative Stress, Induces M1 Macrophage Polarization, and Compromises Myelin Integrity in Skeletal Muscle. Inflammation Research. 2026;75(1):26. (Toriola et al. 2026)
  • DOI:: 10.1007/s00011-025-02158-6
  • PMID:: 41591477
  • Study Design:: Murine experimental model; ATG13 hemizygous deletion (Tg+/-ATG13)
  • Key Findings::
    • ATG13 deficit disrupts autophagy, impairs mitochondrial oxidative metabolism
    • Increased ROS, Sirtuin-1 inactivation via nitrosylation, NF-κB activation
    • M1 macrophage polarization with infiltration into muscle vasculature
    • Myelin integrity loss in nerve bundles innervating muscle
    • Reduced muscle strength after treadmill exercise — PEM-like phenotype
  • Conclusion:: Impaired autophagy can create a PEM-like muscle phenotype with mitochondrial dysfunction, oxidative stress, and neurogenic inflammation. Provides a candidate upstream mechanism for the mitochondrial defects Charlton 2026 documents — the missing link between systemic inflammation and muscle OXPHOS failure.
  • Limitations:: Murine model (single animal); relevance to human ME/CFS not established; same lab group as Drosen 2025.
  • Certainty:: 0.50

8 Behan et al. 1991 — Mitochondrial Abnormalities in Postviral Fatigue Syndrome

  • Full Citation:: Behan WMH, More IAR, Behan PO. Mitochondrial Abnormalities in the Postviral Fatigue Syndrome. Acta Neuropathologica. 1991;83(1):61-65. (Behan, More, and Behan 1991)
  • DOI:: 10.1007/BF00294431
  • PMID:: 1792865
  • Study Design:: Cross-sectional; electron microscopy of vastus lateralis biopsies; n=50 PVFS patients
  • Key Findings::
    • 80% of patients had abnormal mitochondria on EM: branching, elongation, compartmentalization of cristae, paracrystalline inclusions
    • Type II fibre atrophy predominant
    • Findings were present in all patients regardless of symptom duration
    • Controls (n=20) had normal mitochondria on EM
  • Conclusion:: First study to demonstrate structural mitochondrial pathology in post-viral fatigue syndrome — published 35 years before Charlton 2026 but fundamentally consistent with the finding of mitochondrial dysfunction as disease-intrinsic, not deconditioning-driven.
  • Limitations:: 1990s methodology (no quantitative stereology, no respirometry); diagnostic criteria not modern (Oxford definition); no ME/CFS-specific recruitment.
  • Certainty:: 0.35

References

Behan, W. M. H., I. A. R. More, and P. O. Behan. 1991. “Mitochondrial Abnormalities in the Postviral Fatigue Syndrome.” Acta Neuropathologica 83 (1): 61–65. https://doi.org/10.1007/BF00294431.
Charlton, Braeden T., Anouk Slaghekke, Brent Appelman, Moritz Eggelbusch, Jelle Y. Huijts, Wendy Noort, Paul W. Hendrickse, et al. 2026. “Skeletal Muscle Properties in Long COVID and ME/CFS Differ from Those Induced by Bed Rest.” Nature Communications. https://doi.org/10.1038/s41467-026-75725-y.
Eggelbusch, Moritz, Braeden T. Charlton, Alessandra Bosutti, Bergita Ganse, Ifigeneia Giakoumaki, Anita E. Grootemaat, Paul W. Hendrickse, et al. 2024. “The Impact of Bed Rest on Human Skeletal Muscle Metabolism.” Cell Reports Medicine 5 (1): 101372. https://doi.org/10.1016/j.xcrm.2023.101372.
Germain, Arnaud, Katherine A. Glass, Mary A. Eckert, Ludovic Giloteaux, and Maureen R. Hanson. 2025. “Temporal Dynamics of the Plasma Proteomic Landscape Reveals Maladaptation in ME/CFS Following Exertion.” Molecular & Cellular Proteomics 24 (12): 101467. https://doi.org/10.1016/j.mcpro.2025.101467.
Hendrickse, Paul W., Rob C. I. Wüst, Bergita Ganse, Ifigeneia Giakoumaki, Jörn Rittweger, Alessandra Bosutti, and Hans Degens. 2022. “Capillary Rarefaction During Bed Rest Is Proportionally Less Than Fibre Atrophy and Loss of Oxidative Capacity.” Journal of Cachexia, Sarcopenia and Muscle 13 (6): 2712–23. https://doi.org/10.1002/jcsm.13072.
Joseph, Phillip, Claudia Arevalo, Rudolf K. F. Oliveira, Mariana Faria-Urbina, Aaron B. Waxman, and David M. Systrom. 2021. “Insights from Invasive Cardiopulmonary Exercise Testing of Patients with ME/CFS.” Chest 160 (2): 642–51. https://doi.org/10.1016/j.chest.2021.01.082.
Singh, Inderjit, Phillip Joseph, Paul M. Heerdt, Marjorie Cullinan, Denyse D. Lutchmansingh, Mridu Gulati, Jennifer D. Possick, and David M. Systrom. 2022. “Persistent Exertional Intolerance After COVID-19: Insights from Invasive Cardiopulmonary Exercise Testing.” Chest 161 (1): 54–63. https://doi.org/10.1016/j.chest.2021.08.010.
Toriola, M. A., E. Timlin, S. Bulbule, A. Reyes, O. M. Adedeji, C. G. Gottschalk, A. Barua, L. A. Arnold, and A. Roy. 2026. “Genetic Depletion of the Early Autophagy Protein ATG13 Impairs Mitochondrial Energy Metabolism, Augments Oxidative Stress, Induces M1 Macrophage Polarization, and Compromises Myelin Integrity in Skeletal Muscle.” Inflammation Research. https://doi.org/10.1007/s00011-025-02158-6.