Capturing the post-exertional exacerbation of fatigue following physical and cognitive challenge in patients with chronic fatigue syndrome

Abstract

Objective: To design and validate an instrument to capture the characteristic post-exertional exacerbation of fatigue in patients with chronic fatigue syndrome (CFS). Methods: Firstly, patients with CFS (N = 19) participated in five focus group discussions to jointly explore the nature of fatigue and dynamic changes after activity, and inform development of a self-report instrument - the Fatigue and Energy Scale (FES). The psychometric properties of the FES were then examined in two case-control challenge studies: a physically-demanding challenge (moderate-intensity aerobic exercise; N = 10 patients), and a cognitively-demanding challenge (simulated driving; N = 11 patients). Finally, ecological validity was evaluated by recording in association with tasks of daily living (N = 9). Results: Common descriptors for fatigue included 'exhaustion', 'tiredness', 'drained of energy', 'heaviness in the limbs', and 'foggy in the head'. Based on the qualitative data, fatigue was conceptualised as consisting of 'physical' and 'cognitive' dimensions. Analysis of the psychometric properties of the FES showed good sensitivity to the changing symptoms during a post-exertional exacerbation of fatigue following both physical exercise and driving simulation challenges, as well as tasks of daily living. Conclusion: The 'fatigue' experienced by patients with CFS covers both physical and cognitive components. The FES captured the phenomenon of a post-exertional exacerbation of fatigue commonly reported by patients with CFS. The characteristics of the symptom response to physical and cognitive challenges were similar. Both the FES and the challenge paradigms offer key tools to reliably investigate biological correlates of the dynamic changes in fatigue.