eli5 Why can’t humans sprint a marathon?
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Sprinters use anaerobic respiration which releases toxic lactic acid into the body around the muscles and needs to be removed or changed shortly after so sprinting can only last for a few seconds.
Sprinting essentially means running as fast as you can, naturally humans can’t run as fast as they can for 26 miles.
The reason sprinting is essentially impossible to do for more than 200 yards is because of lactic acid buildup in your muscles.
Lactic acid is a byproduct of the chemistry that makes your muscles function. The more they function the more lactic acid is built up, and if they are not given enough time to get rid of the lactic acid, your body’s muscles will eventually stop working properly for a time because the precise chemical balance needed for your muscles to function is thrown off.
It’s like a car, if a car is driven at top speed for long enough the engine will get too hot and it will stop working.
All things need balance.
You might ask why we aren’t built to run faster for longer? That’s because of evolution.
Evolution only cares about an animal being good enough to survive, and we can run fast enough to survive as is
Other replies are good but also miss my the point of energy production.
Everything in our body requires something call adenosine 5- triphosphate or ATP to work. ATP is literally what makes us live. We have two types of metabolism: aerobic, or with oxygen, and anaerobic, with out oxygen. Aerobic is the normal state of our body. It’s when the max amount of oxygen is binding to our red blood cells and perfusion (oxygenation of the cells) is happening at a consistent rate. When we are using an aerobic metabolism, the cellular respiration produces 36 ATP while anaerobic only produces 2 ATP. All this is related to many different systems in the body including glucose levels, sodium and potassium, fluid shift, just a lot of things. But the basic concept to understand is we produce a lot more energy when we have the correct amount of oxygen in our system. When you run and exercise, your heart rate increases, your respiratory rate increases and the total amount of oxygen being retained and sent through out your body is reduced. Reduction of oxygen = reducing of ATP produced = less effective performance from cells = degradation of cells = death. Like someone said before, with the car example, is kinda correct except i would say it more like going 100mph is going to drain your gas tank a lot faster then going 30mph, if that make sense?
Metabolic states is a super interesting topic. And your seemingly simple question gets into a lot of different topics that include acid-base balance, perfusion (I think it’s called the Fink principle)fluid balance, the whole 9 yards.
I also remember reading something about how humans are designed or evolved to be essentially plodding long distance runners. Like we just used to tire our prey out by chasing it. Kinda like how the villain in horror movies only has to walk ya know?
probably a great example of this is cycling, team events… some teams have great sprinters who can put a huge amount of force into the pedals and can go past what most people would consider normal limits, these sprinters will go deeeeeeeeeeeeeeep into the red, pushing their bodies limits way past what is sustainable for any prolonged period of time. they are a mess after the sprint
to get their sprinter to the line teams do lineouts, they have big engine humans who can do turns at a fast pace for maybe 30 seconds to 1 minute… a dude who can do a slightly less high pace for 1minute to two minutes etc… teamies who will control the pace for an hour before that so their sprinter will be in peak condition as they get to the end. they all ride at the limit of what they can sustain. its fast, but they could go faster for shorter periods.
they all do their turn in getting their sprinter as close to the line as possible in peak condition so he can then do his few seconds he can go deep into the red and contest the sprint over the last few to a few hundred metres in a 150km race
you can only go so deep into the red for so long. you can probably run fast for a long time with enough training, but you can only sprint so long before your body just up and nopes out.
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