Mitochondrial stress test conducted using glucose (10 mM) as a substrate in skeletal muscle cells from CFS patients (n = 9) and healthy controls (n = 11). Cells were untreated (white bars), treated with 1 µM compound 991 for 2 h (hatched bars), or treated with 2 mM metformin for 16 h (diagonal bars). (A) Basal respiration. (B) Basal respiration relative changes. (C) ATP production. (D) ATP production relative changes. (E) Maximal respiration. (F) Maximal respiration relative changes. (G) Whole mitochondrial stress test trace in untreated cells. OCR oxygen consumption rate; HC healthy control; CFS CFS patient. Relative changes were calculated for each individual samples and compared to their untreated reading for each parameter. Groups were compared using two-way ANOVAs followed by post-hoc Bonferroni correction. *p < 0.05; **p < 0.01; ***p < 0.0001. a = differs significantly from untreated.