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?
​
edit: first time posting here and this sub does not disappoint, thanks for such quick responses!
In: 2
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.
If it is warmer you need to pump more blood to the skin to lose the heat your body produces. How much the temperature of the blood drops when it flows in your skin depends on the temperature difference between your body and the surroundings.
At the same time, you need to transport blood to the muscles to provide oxygen. Muscles can cheat and get energy without oxygen, then Lactic acid is produced, But to a higher level makes the muscles harder to move and too much would kill you. You get rid of it with oxygen, this is why not ned to breathe a lot directly after hard work, you need oxygen to remove the Lactic acid.
The heart has a limited pumping capacity and it is want in many ways limits your performance. If you are at max heart capacity you get less blood to the muscles compared to in colder weather. It results in the low sustained energy output of being reduced.
If you are not at max capacity you can still supply all oxygen to the muscles but the heart needs to work harder than in cold weather because of the extra flow to the skin.
If you work above sustainable capacity the Lactic acid will build up faster in warm weather.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2375553/
Okay, imagine your body is like a car, and your muscles are the engine that makes the car go. When you exercise, your muscles need energy, and they get this energy from the food you eat.
Now, when it’s really hot outside, your body has to do extra work to keep cool. It’s like the car’s engine getting really hot. So, some of the energy that your muscles need to exercise is used to cool down your body instead.
Think about it like this: when you exercise, you have a lot of energy, right? But if it’s super hot in your room, you might start feeling tired faster because some of your energy is used to stay cool and not get too hot.
So, in higher heat, it’s harder to exercise because your body has to use some of its energy to stay cool, which leaves less energy for your muscles to work and move. That’s why you might feel tired more quickly when it’s really hot outside.
When you use your muscles, your body uses glucose and oxygen to create adenosine triphosphate (ATP), which essentially then breaks down into adenosine, phosphate, and the energy your cells use to create movement. This release of energy is done in two main parts: Kinetic energy, which is motion energy that actually makes you move, and thermal energy, which is heat.
Your body needs to release this thermal energy, or it would otherwise overheat, which causes the breakdown of essential proteins in your brain, heart, and other places. The human body’s main mechanism to get rid of excess heat is sweat. Sweat is mostly water (around 98%), and the rest is sodium, which comes from salt, and broken down fat. This sweat is secreted from glands in your skin, which then evaporates. Simply speaking, when sweat evaporates, it takes heat with it.
In a sedentary state, your body spends about half of your daily caloric intake on regulating its temperature. You spend more energy every day keeping your body in that 36-38 degree Celsius (97-99 degree Fahrenheit) range than any other singular bodily function, including digestion. Sweating and the release of bodily heat, which is part of this so-called thermal regulation, uses a very large amount of energy.
This being said, when it’s cool outside, your body heats up slower during exercise than it does if it’s hot. Therefore, you have to spend less energy sweating, which gives you more energy to activate your muscles and propel yourself forward. Wind accelerates the cooling effect that sweating brings by more rapidly evaporating the sweat off your skin. This is the reason why, for instance, when you’re outside on a hot day and a breeze blows past you, you feel an instant wave of relief from the heat. The wind rapidly evaporated the sweat off you, causing all that heat to get taken away.
Unless you are extremely conditioned, meaning you have trained your body to act and function in certain manners, your body can’t just use unlimited energy to simultaneously cool yourself down and commit to high energy physical activity in high heat. In higher heat, this means that your body redirects energy from your muscles to your autonomic nervous system, which is responsible for making you sweat. This redirection of energy is what makes you feel exhausted more quickly when running in higher temperature — you physically cannot surpass your body’s automatic response to the stress placed upon it by physical exertion.
Elite runners, such as marathon runners or those who run in hot climates, have dedicated significant time and energy towards training their bodies to withstand more extreme environments. This training is the reason why they can run for extended periods, at higher speeds, in higher temperatures. Of course, genetics plays a role, but that’s a discussion for a different time.
The mechanism is that your cells start to die when your internal temperature gets too high. That’s why fevers are dangerous, but you can harm yourself by overheating from exercise or being out in extreme heat.
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.)
It’s not so much heat but the humidity. I lived in Canary Islands and running by the seaside was lovely but now that I live in Lombardia which has comparable humidity to London and the high temperature on top of that it took me a sec to readjust
Latest Answers