a meta-analysis is only as good as the research ingredients that go into it, I was interested to see the results published by Bryan Loy and colleagues  who concluded that: "preliminary evidence indicates that acute exercise increases fatigue in people with ME/CFS/SEID more than in control groups, but effects were heterogeneous between studies."
ME - myalgic encephalomyelitis - and CFS - chronic fatigue syndrome - are conditions that I'm interested to talk about on this blog; specifically how after seemingly years and years in the research-clinical wilderness, science is starting to put some real effort into determining cause(s) and importantly, what might be done about ameliorating this quality of life-crushing condition. SEID - systemic exertion intolerance disease - by the way, is a rather newer description of symptoms (just in case you were not already confused enough).
Loy et al set about combing the peer-reviewed research literature for studies pertinent to their examination of the "population effect of a single bout of exercise on fatigue symptoms in people with ME/CFS/SEID." Interestingly, Google Scholar and not PubMed was there search engine of choice, where 7 studies "examining 159 people with ME/CFS/SEID met inclusion criteria" went on to be included for study. After some statistical analysis, authors concluded that: "Fatigue increases were larger for people with ME/CFS/SEID when fatigue was measured four or more hours after exercise ended rather than during or immediately after exercise ceased." They also suggested that more precise research is required in terms of the effects of exercise on this population.
If, like me, you assume that quite a lot of people who have been included under the headings of ME/CFS/SEID are actually suffering (yes, suffering) with an organic illness/illnesses  potentially affecting the way energy is created, stored or used in the body, such results are probably not unexpected. Words like 'mitochrondrial issues' are not totally unfamiliar to at least some parts of the ME/CFS/SEID continuum (see here and see here) and given the link between mitochondria and energy, may well provide at least one answer why post-exertional fatigue/malaise is present for some. The idea of immune system involvement in ME/CFS/SEID cannot also be left out of the equation (see here) although the precise relationship to fatigue is slightly less clear-cut.
I'd agree with the authors that more needs to be done on the hows and whys of post-exertional fatigue following acute exercise in this patient group including why other reviews  have reported contrary findings when it comes to exercise therapy lasting "from 12 to 26 weeks." And before you mention, yes, I'm well aware of the various goings-on with regards to a certain trial for CFS where exercise of the graded variety was used...
Of course acute exercise vs. chronic exercise (if I can call it that) are not one and the same thing so one has to be slightly cautious of making any direct comparisons. I would however like to see a little more research on the biological processes linked to fatigue post-exercise in this group; as per the suggestion by Rutherford and colleagues  that: "Bioenergetic muscle dysfunction is evident in CFS/ME" and what implications this might have. That also a few other favourite topics of mine (gut bacteria and bacterial translocation) might also be something to look at (see here) in the area of exercise effects and ME/CFS is worthwhile mentioning too...
 Loy BD. et al. Effect of Acute Exercise on Fatigue in People with ME/CFS/SEID: A Meta-analysis. Med Sci Sports Exerc. 2016 May 17.
 Edwards JC. et al. The biological challenge of myalgic encephalomyelitis/chronic fatigue syndrome: a solvable problem. Fatigue. 2016 Apr 2;4(2):63-69.
 Larun L. et al. Exercise therapy for chronic fatigue syndrome. Cochrane Database Syst Rev. 2015 Feb 10;2:CD003200.
 Rutherford G. et al. Understanding Muscle Dysfunction in Chronic Fatigue Syndrome. J Aging Res. 2016;2016:2497348.
Loy BD, O'Connor PJ, & Dishman RK (2016). Effect of Acute Exercise on Fatigue in People with ME/CFS/SEID: A Meta-analysis. Medicine and science in sports and exercise PMID: 27187093