Good physical as well as cognitive functioning have a positive influence on the performance of activities of daily living. Patients with chronic fatigue syndrome (CFS) as well as patients with fibromyalgia have significant cognitive deficits. In addition, a good physical and functional health status may have a positive impact on a variety of cognitive skills—a link that has been observed in young and old individuals who are healthy, although evidence is limited in patients with CFS. This study’s aim was to investigate whether recovery of upper limb muscle function could be a significant predictor of cognitive performance in patients with CFS and in patients with CFS and comorbid fibromyalgia. Furthermore, this study determined whether cognitive performance is different between these patient groups. Seventy-eight participants were included in the study: 18 patients with CFS only (CFS group), 30 patients with CFS and comorbid fibromyalgia (CFS+FM group), and 30 individuals who were healthy and inactive (control group) were studied. Participants initially completed 3 performance-based cognitive tests designed to assess selective and sustained attention, cognitive inhibition, and working memory capacity. Seven days later, they performed a fatiguing upper limb exercise test, with subsequent recovery measures. Recovery of upper limb muscle function was found to be a significant predictor of cognitive performance in patients with CFS. Participants in the CFS+FM group but not those in the CFS group showed significantly lower cognitive performance compared with the control group. The cross-sectional nature of this study does not allow for inferences of causation.
The findings of this study indicate that better physical health status could predict better mental health in patients with CFS. Furthermore, they underline disease heterogeneity, suggesting that reducing this factor in future research is significant in better understanding and uncovering mechanisms regarding the nature of diverse impairments in these patients.