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

The problem is that your body have a hard time getting rid of excess heat. Whenever you move a muscle it generates heat and your body needs to get rid of this heat some way. But when it is hot this can be hard. So first the body have a natural instinct to slow you down by making you tired. This is basically your body trying to prevent you from overheating. If this does not cool you down, for example if you are trying to push through it, then the heart actually changes its rhythm as you heat up. Instead of strong long pulses which are good at pumping lots of blood from your lungs to your muscles the heart switches to weaker shorter pulses to get your heart rate even higher. This higher pulse makes the blood flow more constant so that you get a constant blood flow through your skin which helps cool down the body. But it reduces the flow of oxygen rich blood to your muscles so you start building up lactic acid and your muscles have less energy. If you get to the point where you notice this then you should slow down and get first aid for heat stroke immediately. If not then the next thing which will happen is that the blood vessels near your skin will become bigger to allow more blood to your skin rather then your muscles. This will drop the blood pressure even further and reduce the blood flow to your muscles even more. If you notice this then you should call an ambulance and get checked out by a doctor afterwards. The next symptoms of heat stroke is basically your neural system starting to break down.

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