Disclaimer: this discussion will not make you a faster cyclist. It might even get you kicked out group rides if you discuss it. That said, exercise physiology is cool and some people might find it of interest.
I came across a paper discussion the splenic changes during acute sub-maximal (60% VO2 max) and maximal exercise (graded ramp to exhaustion). The spleen helps to remove aging RBCs out of systemic circulation, but also serves as a small blood cell “bank”. I failed to recognize the relatively large increase in circulating RBCs (along with platelets and WBCs) released from the spleen during acute exercise. Splenic volume decreases by ~ 60% during exercise and recovers fairly rapidly during recovery (within 20 minutes). The relative contribution to circulating RBCs is variable based on the estimate of the spleen volume with ranges from 1.5% to 10% increase in RBC count during exercise, but even 1.5% could be associated with an increase in exercise performance. The increase in RBC count partially contributes to the increase in hematocrit with exercise (along with decreased plasma volume). Disappointing to me, aerobically trained athletes did not have larger spleens as this would have been an interesting training adaptation. That said, no one has studied the inter-individual variability in spleen mass on exercise performance. Fun fact, some animals such as seals and horses store ~50% of their RBCs in the spleen during inactivity. Running performance is decreased in horses post-splenectomy. For any individuals with extra time that are interested in looking at this older article, it can be found here: Cardiovascular and splenic responses to exercise in humans - PubMed
Well, you certainly have given me something to research! I am now 46, but had a splenectomy when I was 20. I seldom give it a thought, but I wonder what effect that has on my performance. Down the rabbit hole I go…
@Alen, did you read the manuscript in its entirety? The manuscript does not claim an ergogenic role of the spleen, just explains the physiology. What is your critique? Why do you think that it is junk science?
The primary role of the spleen is hematological and secondarily immunological. There is absolutely nothing about the spleen to augment positively or negatively an exercise. In the case of someone missing a spleen the bone marrow stake over the hematological role.
As for it shrinking in size and supplying more plasma and RBC’s into the bloodstream, that pretty much happens to every organ during exercise. Blood is shunted away from GI system and skin and increased into the muscular system. That’s why you can’t absorb food well with higher intensity. For the article trying to suggest that this phenomenon is special to the spleen is misleading.
Would be interpretation for me. As Alen said, a bunch of organs get larger or smaller during exercise. This doesn’t mean they play a role in performance. The spleen has no aerobic requirements, therefore, vasculature shunts blood a way. They also claim that plasma catecholamines are “related” meaning there’s a brute correlation between the two, but then they interpret this to mean that catecholamines are the cause, which is not at all a good assumption - I could just as easily claim a shrinking spleen drives catecholamine production. Overall, they show a few sparse correlations and no actual evidence that it matters for performance and then conclude by drastically overinterpreting minor results that prove nothing. And that’s just from reading the abstract.
This paper was from 2001. There are more recent papers that have found similar findings. Some have suggested that increased inta-abdominal pressure stimulates the release of blood cells. Other animals (i.e. mice) sequester erythrocytes in organs other than the spleen (liver). Using technetium, we only observe erythrocytes sequestration in the spleen and lungs. Your interpretation that that a 1.5% increase in systemically circulating RBCs is not associated with a statistically significant increase in the RQ as submaximal workloads or a shift in the lactate threshold. That was not tested. To be fair to the authors, they don’t postulate an aerobic performance enhancement with the increased number of circulating RBCs. I added that to stimulate conversation. I appreciate that you read the paper and offered your critique. That is one of the many strengths of our community.
For sure. I probably came off overly aggressive, but it was more because I got annoyed on a professional basis with the authors’ own over interpretations in the conclusion of the abstract. Obviously all studies have limitations and I did think the part about seals and horses was interesting, although unlikely to be true for humans just based on the size of the organs. Although it might be interesting to consider the relative importance of the spleen as a reservoir for RBCs compared to other organs such as skin and GI tract that also have blood shunted from them during exercise.