Decreased oxygen extraction during cardiopulmonary exercise test in patients with chronic fatigue syndrome (available as Free Full Text – link at end)
Low oxygen uptake by muscle cells causes exercise intolerance in a majority of CFS patients, indicating insufficient metabolic adaptation to incremental exercise. The high increase of the cardiac output relative to the increase of oxygen uptake argues against deconditioning as a cause for physical impairment in these patients.
Cort Johnson explains in more detail:
Oxygen means everything for exertion in humans. If you want to be able exercise vigorously you’ve got to get oxygen (and lots of it) into the mitochondria of your muscles.
Seventy percent of the CFS and the CFI patients had significantly lower maximal oxygen uptake (VO2 max) at anaerobic threshold than the controls.
the lowest muscle oxygen uptake achieved by the healthy controls at maximal workload was a very low 10 ml/100 mls, a value Vermoulen reported is found in heart failure
the lowest oxygen uptake by the ‘CFS’ (Fukuda) patients was less than half that of the worst off control (4.4 ml/100 mls.) o
the muscles of that patient was receiving about 44% of the oxygen that the poorly functioning healthy control was.
The sheer size of this study would, one would think, effectively end the question whether metabolic abnormalities thwart energy production during exercise in ME/CFS, or whether deconditioning is a significant factor.
Satisfied that metabolic impairment is present, exercise physiologists are moving forward to try and discern its cause.
Here’s the full PubMed article:
The lower maximal exercise capacity (peak V’O2) of CFS and CFI patients was related to a lower oxygen uptake of the muscle cells (C(a-v)O2) and a higher increase of cardiac output relative to V’O2 (ΔQ’/ΔV’O2) than in healthy men and women.
The stroke volume and cardiac output increased during the exercise test, but at no level of effort a consistent difference was seen between the three groups, indicating a normal adaptation of the heart to increasing workload in CFS patients.
This retrospective study showed that a low oxygen extraction and a high ΔQ’/ΔV’O2 were consistent with a metabolic cause for exercise intolerance in 70% of CFS patients.