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1) Spanish researchers exposed muscle cells to serum of ME/CFS and Long Covid patients and found: - reduction in muscle contraction strength - upregulation of genes involved in protein translation - elevated oxygen consumption

2) It looks like the 'something in the blood' hypothesis is back on the table: serum of patients caused cellular stress that serum of healthy controls did not. The sample size was really small though: serum of only 4 ME/CFS patients and 5 Long Covid patients was used.

3) The researchers developed 3D skeletal muscle tissue in the lab and exposed it for 48 hours to sera of patients (ME/CFS and LC patients) or controls. They replicated the experiment a couple of times per serum sample (these are probably the white open dots in the graphs).

4) The graph below shows the results for maximum contractile force, indicating that the muscle tissue had less strength if they were exposed to ME/CFS or LC serum.

5) The authors used RNA sequencing to get a glimpse of the activity happening in the muscle cells. There was upregulation of genes involved in protein translation and extracellular matrix and downregulation of those involved in basic organelle functions.

6) They also found that muscle fibers became larger (hypertrophy) and that mitochondria fused together into different shapes. According to the authors, this all points to cellular stress and altered metabolic activity caused by ME/CFS and LC serum.

7) When they exposed the muscle cells to serum of patients for a longer period (96–144 hours), they found it caused muscle fragility and weakness, with mitochondria fragmenting.

8) This study also reports an increase in the overall oxygen consumption rate which seems to contradict findings from a bigger study that failed to replicate the 'something in the blood' hypothesis and reported no difference in oxygen consumption. www.biorxiv.org/cont...