Sex differences in post-exercise fatigue and function in myalgic encephalomyelitis/chronic fatigue syndrome 2023 Friedberg et al

Abstract

To assess biobehavioral sex differences in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) utilizing a low burden exercise protocol, 22 females and 15 males with ME/CFS and 14 healthy controls underwent two six-min walk tests. Fifteen daily assessments were scheduled for fatigue and function ratings and heart monitoring. Six-min walk tests were conducted on days 8 and 9. The ME/CFS group showed high self-report fatigue and impaired physical function, whereas healthy controls did not show fatigue or function abnormalities. In patients, no significant post-exercise changes were found for heart rate variability (HRV); however, heart rate decreased in ME/CFS males from Day 14 to Day 15 (p = 0.046). Female patients showed increased fatigue (p = 0.006) after the initial walk test, but a downward slope (p = 0.008) in fatigue following the second walk test. Male patients showed a decrease in self-report work limitation in the days after exercise (p = 0.046). The healthy control group evidenced a decrease in HRV after the walk tests from Day 9–14 (p = 0.038).

This pilot study did not confirm hypotheses that females as compared to males would show slower exercise recovery on autonomic or self-report (e.g. fatigue) measures. A more exertion-sensitive test may be required to document prolonged post-exertional abnormalities in ME/CFS.

Open access, https://www.nature.com/articles/s41598-023-32581-w

 

The conclusion seems sensible. It boils down to the question of finding a balance between an exertion test that elicits detectable biological changes but is untolerable, and, as in this study, a more tolerable test that does not elicit these changes.

The issue is that the observed differences on the parameters of the 2-day CPET between ME/CFS patients and controls are already small, so does an alternative really exist? Perhaps advances in the pathophysiology of PEM will enable us to find the specific type of exertion that is needed to trigger it, and from there develop a test that causes minimal but detectable PEM. For now, this study unfortunately confirms that we have no better tool than the 2-day CPET.