Research abstract:


To design and validate an instrument to capture the characteristic post-exertional exacerbation of fatigue in patients with chronic fatigue syndrome (CFS).


  • Provides a new self-report measure of fatigue in patients with chronic fatigue syndrome
  • Uniquely captures fatigue in real time with descriptive anchors derived from focus groups
  • Captures exacerbations following challenge tasks in the laboratory and in daily living
  • Distinct scale domains capture exacerbations following physical and cognitive tasks.


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).


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.


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.

Capturing the post-exertional exacerbation of fatigue following physical and cognitive challenge in patients with chronic fatigue syndrome, by A Keech et al in Journal of Psychosomatic Research, 2 September 2015 [Epub ahead of print]

Simon McGrath from Phoenix rising comments:

There are a number of things I really like about this study:

  • Focus on post-exertional, not general fatigue, and ‘challenge’ tests of both moderate exercise and a driving simulator a cognitive challenge. I’d like to see a lot more studies using this approach
  • Involvement of patients in discussing what should be  in the fatigue scale (by contrast, Simon Wessley said he came up with the fatigue questions for the Chalder Fatigue scale all by himself).
  • The descriptors for post-exertional fatigue seem – from memory- similar to those that came up in studies by Lennny Jason and colleagues.

I wish they’d looked at post-exertional malaise more generally, rather than just focusing on fatigue. And while this study seems like a good start I don’t think you can validate any questionnaire on such a small sample. Added: the authors acknowledge this: “While the analysis of the psychometric properties of the FES was conducted across several patient groups and assessment conditions, each analysis involved only small samples of patients with CFS; investigation of the validity and reliability of the instrument in larger samples, and especially in patients with more severe symptomology, is required”.

This paper is part of a series using the challenge tests (another one here), and I know of two others that sound pretty interesting, including one that aims to replicate work done elsewhere.

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