what is the actual mechanism that makes it harder to exercise in higher heat?

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Compared to jogging in high 60s/low 70s (F) with a slight breeze and partial clouds, jogging in mid-80s (F) no breeze full sun means a worse pace and also much harder struggle to get that worse pace.

When I google online, I get kinda very generic answers: “your body has to work harder to cool” “sweat is less effective” “extra stress on body”, etc but I don’t understand what the actual biomechanics are that make me less capable when I’m working out. Like, OK, if my body has to sweat more, how does that make my muscles less capable of pushing me through a 3-miler? What does the extra stress actually mean? What is actually getting stressed that prevents me from hitting my normal pace?

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edit: first time posting here and this sub does not disappoint, thanks for such quick responses!

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Anonymous 0 Comments

Your body doesn’t actually have enough blood to supply all your organs with the amount they need to work at maximum capacity. So it always has to prioritize. This is why, for instance, it’s hard to do physical exercise shortly after eating, or indeed to digest things while exercising. Your body can send blood either to your digestive system or to your muscles, but not both. So if you go for a run straight after a meal, your digestive system will complain because it isn’t getting enough blood to do what it needs to do.

(To clarify, it’s not that there’s (normally) ever *no* blood going to certain organs. There’s always some – enough to keep the organs alive and healthy. But your muscles need a lot more blood to power you through a run than they do to just hang out and not die. And your gut needs a lot more blood to digest a meal than it does to just chill out and survive.)

Now, your skin is also an organ – in fact it is the largest organ in the whole body. One important job it has is to cool you down when you’re at risk of overheating. To do this, blood has to pass through the skin so that it can dump its heat to the environment. And the more blood goes to the skin, the less is available to go to supply your muscles with the oxygen they need for exercise.

(The way this works, by the way, is that blood vessels constrict in some places and open up (*dilate*) in other places. Your heart is just pumping away and doesn’t know where the blood is going, but it flows more easily to places where the blood vessels are open wide, while less of it reaches places where the blood vessels are more constricted.)

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