This US pilot study was surprised to find that a six-minute walk test didn’t produce as many post-exercise abnormalities in people with ME/CFS and no major differences between men and women.

Healthy people’s hearts returned to a slow rate in the 7 days after the walk tests, whereas the ME/CFS group showed no significant change.

It is uncertain how much physical exercise over how many days is required to sustain PEM. The researchers suggest that a 12-min walk test with instructions to “walk as fast as you can” would be produce more results and would enable many disabled ME/CFS patients, who lack mobility to participate in research from home.


Sex differences in post-exercise fatigue and function in myalgic encephalomyelitis/chronic fatigue syndrome, by Fred Friedberg, Jenna L Adamowicz, Patricia Bruckenthal, Maria Milazzo, Sameera Ramjan, Xiaoyue Zhang & Jie Yang in Scientific Reports vol 13, no: 5442, 3 Apr 2023

Research 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.


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