No deconditioning or abnormal muscle function - but more effort needed and post-exertional fatigue in CFS Exercise performance and fatiguability in patients with chronic fatigue syndrome (Gibson 1993) Another maximal exertion study (n=12): this one didn't use VO2max, unfortunately, but instead measured peak work rate and found no significant difference between Oxford-criteria CFS patients and 'sedentary' controls, concluding They also separately measured function of the thigh muscle and found normal function (same as controls) pre-exercise, but also post exercise inc at 24 and 48 hours. However, unlike controls, the CFS patients did complain of fatigue when rested at 24 and 48 hours. CFS patients have higher levels of perceived exertion Although I'm highlighting it in this study, it's a consistent (though not universal) finding that CFS patients report higher exertion levels at a given heart rate/work load than healthy controls. Handily, exertion has a standard measure: the Borg Rating of Perceived Exertion scale, RPE. There are different way of scoring the scale but this study used 6 (no exertion perceived) to 20 (maximum exertion). While both patients and controls scored 6 at rest, once exercising CFS patients consistently rated their exertion an average of 3.2 points higher than controls. Hardly surprising, and this might be saying something important about the illness. The authors instead stalk of the need to test the ability of exercise to 'reset the effort perception thershold' in CFS.