The Conversation: VO₂max: the gold standard for measuring fitness explained

Ravn

Ravn

Senior Member (Voting Rights)
Mostly an article by sports scientists exhorting us all – well, maybe not us specifically – to exercise more. However, the article mentions an interesting working hypothesis (no published papers on this that I could find, not looking very hard though). Bolding mine.

The logical question to ask is why VO₂max is so important for long-term health. This question has largely been ignored by researchers, and there are no clear answers. In our research, our working hypothesis is that VO₂max is a proxy for the amount of blood in the body. A greater volume of blood allows more oxygen to be transported to the muscles and so leads to a higher VO₂max.
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https://theconversation.com/vo-max-the-gold-standard-for-measuring-fitness-explained-109486

If we assume for a moment the hypothesis is correct, how would that fit in with 2-day CPET results where PwME typically have near normal VO2max on day 1 but significantly lowered VO2max on day 2? Surely we don't have a significant amount of blood going awol overnight?
 
Ravn said:
If we assume for a moment the hypothesis is correct, how would that fit in with 2-day CPET results where PwME typically have near normal VO2max on day 1 but significantly lowered VO2max on day 2? Surely we don't have a significant amount of blood going awol overnight?
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Seems wrong to me, there is an association with blood volume, but it is not the only association.

It is intriguing though as my major PEM symptoms are circulation related.

The performance drop on the 2 day CPET in ME patients is primarily lower power at the ventilatory threshold, rather than a drop in VO2... The reason why some patients cannot reach their prior VO2max is due to leg fatigue - the legs simply are not putting out the same power at the same level of neural drive (which is directly related to effort perception) anyone who has done the test will know this. The reason why some patients are able to match their prior VO2peak is because they didn't actually reach VO2max on the first day.
 
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From
https://us.humankinetics.com/blogs/excerpt/dehydration-and-its-effects-on-performance

Fatigue toward the end of a prolonged sporting event may result as much from dehydration as from fuel substrate depletion.
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Even in cool laboratory conditions, maximal aerobic power ( .VO2max) decreases by about 5% when persons experience fluid losses equivalent to 3% of body mass or more, as is shown in figure 8.6 (Pinchan et al. 1988). In hot conditions, similar water deficits can cause a larger decrease in .VO2max.
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So, dehydration lowers VO2max. It's interesting, given how people with ME have said they feel better with saline infusions and (I think) medications for orthostatic intolerance that increase blood volume.

Could it be that, after exertion, fluid that should be in the circulation system is pooling elsewhere e.g. in the lower legs and abdomen?
 
There have been some further questions and answers by one of the authors that some may find interesting.

The conclusion is that while haematological factors are central to VO2Max, blood volume might not always be the rate limiting factor.

One of the authors suggested that peripheral factors can be relevant in untrained participants (where training specifically relates to the muscles used in the test) and some testing conditions, VO2Peak can be limited (below VO2Max) by the volume of working muscle and limited peripheral blood flow.
https://www.ncbi.nlm.nih.gov/pubmed/26614395
 
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