Ladek, Anja-Maria, Lucio, Marianna, Weiß, Andreas et al. · Biomedicines · 2025 · DOI
This study looked at oxygen levels in the muscles of 100 people with long COVID and 50 healthy controls while they performed light exercise (squeezing a stress ball). The researchers used a special non-invasive scan called NIRS to measure this. People with long COVID, especially those with post-exertional malaise, showed abnormal oxygen patterns in their muscles compared to healthy people, and this was linked to their fatigue levels.
Many ME/CFS and long COVID patients experience post-exertional malaise with disabling fatigue, and current diagnostic tools are limited. This study provides objective physiological evidence that abnormal muscle oxygenation may underlie fatigue in a subset of patients, potentially opening pathways for better diagnostic testing and targeted treatments tailored to microcirculatory dysfunction.
This study does not establish whether abnormal oxygenation causes fatigue or is merely associated with it; the cross-sectional design cannot determine causality or temporal relationships. It also does not prove that all PCS patients have microcirculatory impairment—only that a subgroup may, and does not evaluate whether NIRS measurements can predict treatment response or disease progression.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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