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I've read several fitness articles mentioning redirected blood flow to muscles that are in use. However, they never mention how it works. Is it local and specific to the muscles in use? Or, for example, I guess more blood has to flow through the entire arm if I am training my forearms..? So, won't the entire arm benefit to a certain extent?

I did some research and discovered the vascular shunt mechanism through the opening and closing of capillary sphincters. However, I cannot find any resources discussing how local this effect is. So, as an example, how much does blood flow to the arm improve if someone is training their forearm for six months?

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  • $\begingroup$ I'm voting to close this question as off-topic because this is a biology site not a sports training site. $\endgroup$
    – David
    Commented Apr 8, 2019 at 18:44
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    $\begingroup$ @David Well I originally posted this at the physical fitness SE. They apparently felt it belonged here, and it got migrated. So, apparently it's too technical for them and too sports related for you. I clearly need to edit this question to make it belong in one of the SEs. $\endgroup$
    – Avatrin
    Commented Apr 9, 2019 at 4:55
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    $\begingroup$ I think could be on topic, though it should be changed to keep it on-topic here: 1) Your question contains aspects of both acute (immediate) changes during exercise and also chronic (long-term) changes. It would be better if your question focused on one or the other to focus on a specific biological question. We like questions that have some prior research here, too. 2) The background on conditioning/training is a bit problematic, because some people might interpret the question as asking for personal advice. $\endgroup$
    – Bryan Krause ♦
    Commented Apr 15, 2019 at 23:11
  • $\begingroup$ @BryanKrause Alright, thanks for the feedback! I have now tried editing it to make it on-topic for the biology SE. $\endgroup$
    – Avatrin
    Commented Apr 16, 2019 at 7:53

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A major determiner of blood flow redirection among muscles is increased oxygen demand in the working muscles.

When a muscle works, it uses oxygen, so the partial pressure of oxygen (PO2) in the muscle falls, which signals small arteries (arterioles) to dilate, which results in increased blood flow and hence oxygen and nutrients delivery to the muscle (Skeletal Muscle Circulation, NCBI Bookshelf).

Picture]([https://www.ncbi.nlm.nih.gov/corecgi/tileshop/tileshop.fcgi?p=BOOKS&id=543677&s=26&r=2&c=2

When you exercise your forearm muscles without exercising upper arm muscles, the arterioles in the forearm muscles will dilate but in the upper arm muscles will not. The blood will just flow through the large arteries of the upper arm toward the forearm, but it won't be delivered to the upper arm muscles.

A long-term effect of exercise is the formation of new capillaries in the exercised, but not in other muscles (PubMed, 2008). So, six months of exercising forearm muscles without exercising upper arm muscles will result in better circulation only in the forearm muscles.

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