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Alex's muscles experience this sensation because his body shifts to anaerobic respiration, a quicker process that doesn't rely on oxygen to generate ATP. Though this method produces significantly less ATP, it skips the longer oxygen-based steps, resulting in faster energy production. Lactic acid is a byproduct of anaerobic respiration, formed when excess oxygen and acetyl CoA from the Krebs cycle accumulate. Along with leftover carbon dioxide, these components create lactic acid, which builds up in the muscles and causes a burning feeling. The cells must then work to remove the lactic acid to avoid fatigue or failure.

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Alex's muscles switch from aerobic to anaerobic respiration between the 400-600m mark. We can observe this as he experiences a burning sensation in his muscles. The reason this happens is because his intake of oxygen from his breathing is no longer able to keep up with the usage in his cells meaning they switch from aerobic respiration to anaerobic respiration. This would lead to the products from the krebs cycle to build up (lactic acid). This creates a burning sensation as while it is not being converted into other products the Lactic acid would start to denature the proteins in the cell which would lower the function of the cell. Alex and other athletes can train to elongate the time for aerobic respiration and delay anaerobic respiration by training the VO₂ max in their body through training more intense cardiovascular activities .

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Alex feels the effects of a large build-up of Lactic Acid in his muscles, causing him to notice particular tightness and soreness in his calves and thighs as well as a burning sensation in his muscles. This is due to long periods of anaerobic respiration. There are 2 types of respiration; Aerobic and Anaerobic respiration. Aerobic respiration is a slower process where glucose goes through a series of reactions in the presence of oxygen to produce 34-36 ATP (A lot of ATP). Anaerobic respiration is an extremely fast process where Glucose is broken down into a net 2 ATP, however, when there is no/little oxygen, a build up of lactic acid occurs. During running, a lot of energy is used. The body switches from Aerobic respiration to anaerobic respiration as energy is produced too slowly with aerobic respiration and there is a lack of oxygen while running fast. He also needs more energy to be able to keep up his fast speed meaning he needs energy in his muscles to be produced faster. This causes anaerobic respiration to occur, where energy is produced very fast, allowing Alex to keep on running. However, the longer he runs fast, the more energy he uses, and the more lactic acid is built up, as, during anaerobic respiration, ATP is produced very quickly, however a build-up of lactic acid occurs. Lactic acid is very acidic and can cause the pH of muscles to drop, causing damage to the cells in the muscles. As he is using his thigh and calve muscles while running, anaerobic respiration occurs there, as energy is being produced there. This means that the lactic acid is also there, causing a build-up of it. Alex finds that he feels a burning sensation and a particular tightness and soreness as there has been a build-up of lactic acid, causing the burning sensation in his muscles and also causing some of his muscles to be slightly damaged due to the drop in pH of the muscles, causing them to slightly break down/denature.

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Aerobic respiration is a cellular reaction in the mitochondria when oxygen is plentiful. Anaerobic respiration is a cellular reaction in the cytoplasm when oxygen is not plentiful. Alex's muscles begin to feel fatigued and a sensation of burning because of the switch from aerobic to anaerobic respiration. During the first 400m of the race, his body has enough oxygen to do aerobic respiration where no lactic acid build-up leads to no pain. After this, his body must respire more quickly to get oxygen to the muscles and it switches to anaerobic respiration. The product of respiring quicker leads to a lactic acid build-up causing pain and tiredness which can lead to a cramp.

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According to https://www.goodrx.com/well-being/movement-exercise/aerobic-vs-anaerobic-exercise, aerobic exercise is when your muscles use the oxygen from the air that you breathe. Also, the oxygen that is produced during aerobic respiration in the mitochondria is used to facilitate the energy requirements that involve Alex's exercise (aerobic respiration produces 34-36 ATP). In aerobic respiration, lactic acid is a product, and when there is a build-up of lactic acid, Alex feels a burning sensation in his muscles because it reduces the pH of the cell and could potentially become toxic. The lack of ATP (2ATP) being produced in anaerobic respiration means that the oxygen supply is inadequate, so the energy needs of the cells are not met. This causes the fatigue that Alex experiences.

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Aerobic vs. Anaerobic Exercise: Which Benefits You More? - GoodRx

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What’s the difference between aerobic and anaerobic exercise, and is one better for you than the other? Join us as we examine both forms of exercise.

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Aerobic respiration occurs with oxygen and releases more energy but more slowly. Anaerobic respiration occurs without oxygen and releases less energy but more quickly.

source = bbc

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Alex’s muscles switch from aerobic to anaerobic respiration when he approaches the final 200 metres. This is because he is not getting enough oxygen so anaerobic respiration takes place. The pyruvate formed in glycolysis breaks down into lactic acid. The physiological consequences for his muscles when undergoing anaerobic respiration is that they become fatigued due to the build up of lactic acid. The lactic acid that is produced can be converted back to glucose.

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Anaerobic respiration occurs during excercise. In the final 200 meters of Alex's race, his body cells stopped getting enough oxygen for aerobic respiration, and therefore anaerobic respiration starts to happen. Anaerobic respiration releases less energy than aerobic respiration, but more quickly. Anaerobic respiration produces lactic acid, and when this builds up it can cause muscle cramps.

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Alex's muscles switch from aerobic to anaerobic, causing Alex to feel a burning sensation and extreme fatigue during a match, because he is receiving less oxygen the more he runs, and therefore switches to anaerobic. Since he has switched from aerobic to anaerobic, he is no longer breaking down glucose, causing a build up of lactic acid, which causes the burning sensation in his legs.

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When Alex works out he could feel out of breath. This is because he is getting an insufficient amount of oxygen necessary for his cells to respire. Therefore, anaerobic respiration occurs. Anaerobic respiration produces 2 ATP per glucose. A consequence of this is the production of lactic acid. Lactic acid fuels you're cells during intense exercise but causes a burning sensation/ muscle fatigue. It breaks down glucose in order to produce sufficient ATP for the cells to function.

https://my.clevelandclinic.org/health/body/24521-lactic-acid

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What is a high lactic acid level?

Health conditions and infections that make it harder for your body to get fresh oxygen to your cells can raise your lactic acid levels. This can lead to lactic acidosis - a dangerously high lactic acid level. Lactic acidosis is a serious health condition that can be fatal.

Lactic acidosis is usually a complication of other health conditions, including:

The most common symptoms of lactic acidosis include:

Nausea and vomiting.

Weakness, especially in your muscles.

Abdominal pain.

If you have lactic acidosis, your body can't process lactic acid fast enough and it starts to damage your organs and tissue. You might vomit as your body tries to remove extra lactic acid as fast as possible.

You can develop lactic acidosis if you push your body beyond its usual limits during a sport, workout or any type of intense physical activity. Working out and playing sports can safely test the limits of your endurance, but don't "play through pain" or force yourself to keep moving when you're physically exhausted.

Lactic acidosis is different than the temporary rise in your lactic acid level after a workout. Typically, your lactic acid level will return to its usual level as soon as you stop an intense physical activity. Your liver and kidneys start breaking the extra lactic acid down right away before you experience symptoms or complications.

What is a lactic acid level test?

A lactic acid level test is a blood test. A healthcare provider will test your lactic acid level if they think you might have lactic acidosis. Your provider will send a sample of your blood to a lab. The lab will check how much lactic acid is in your blood.

Having high lactic acid doesn't automatically mean you have one of the serious conditions that causes lactic acidosis, but it's usually a sign that your cells aren't getting enough oxygen. Your provider will tell you what your results mean and which treatments you'll need to lower your lactic acid level.

Lactate threshold testing for athletes

Some athletes perform a physical test called a lactate threshold test. Athletes use lactate threshold tests to understand the upper limits of their endurance so they can safely train or perform at their highest for as long as possible.

During a lactate threshold test, you'll perform increasingly strenuous exercise while a healthcare provider monitors the level of lactic acid in your blood. They'll take blood samples from you at set points throughout the test to check the lactic acid in your blood in real time.

Never intentionally workout until you're exhausted. Lactate threshold tests must be done under a provider's supervision to make sure you're safe. Talk to your provider if you're interested in a lactate threshold test as part of your training or exercise.

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Lactic acid is a chemical your body naturally produces when your cells break down carbohydrates for energy. It doesn't cause muscle pain or burning.

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When and why do Alex's muscles switch from aerobic to anaerobic respiration during a match or workout? What are the physiological consequences for Alex when his muscles undergo anaerobic respiration?

Areobic respirationis a process of producing energy in cells with the use of oxygen, which breaks down glucose to produce carbon dioxide, water, and a large amount of ATP (around 36 ATP molecules per glucose). Anaerobic respiration is a process of producing energy without the use of oxygen, resulting in the incomplete breakdown of glucose into lactic acid and producing only 2 ATP molecules per glucose. This occurs during exercise, because enough oxygen is abled to supplied to all the cells. When Alex’s muscles switch from aerobic to anaerobic respiration during his run, it means that his oxygen supply is insufficient to meet the energy demands of his muscles. Glucose is broken down into pyruvate molecules, which is then converted into lactic acid due to the lack of oxygen. This lactic acid buildup in the muscles, lowering the pH and inhibiting enzyme activity, which contributes to muscle fatigue. Anaerobic respiration also produces only 2 ATP molecules per glucose molecule, which is far less efficient than the 36 ATP produced during aerobic respiration. This causes Alex’s muscles tire quickly, and he may experience discomfort or cramping due to the buildup of lactic acid.

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During the warm-up and first 400 meters, his body is doing aerobic respiration and has enough oxygen to continue with producing more ATP (34) with no lactic acid build up.

Near the end of his first 400 meters, anaerobic respiration kicks in and starts to quickly produce smaller amounts of ATP (4) and stops using NADP, causing lactic acid build up. The consequences of this for Alex are the build up of lactic acid, which causes muscle pain and fatigue due to build up of lactic acid and lack of larger amount of ATP being produced due to the quicker but less efficient Anaerobic respiration being used.

(Source: My memory)

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His muscles switch from aerobic to anaerobic respiration during a match or workout for him to respire more quickly. During aerobic respiration, oxygen is used and energy is released but more slowly. However he switches to anaerobic respiration, which doesn't use oxygen, and releases more energy, but more quickly.

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(2 people)

The anaerobic energy system produces significantly less ATP than its aerobic counterpart and leads to the build-up of lactic acid.

https://www.physio-pedia.com/Anaerobic_Exercise#:~:text=The%20anaerobic%20energy%20system%20produces,HIIT)%2C%20power%2Dlifting.

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Alex's muscles begin to feel this way because of the switch to anaerobic respiration. This is a faster version of respiration which doesn't use oxygen to produce ATP. From this form of respiration, much less ATP is created but the cell does not need to go through the longer stages, using O2 to produce more ATP - thus making it faster. A product of anaerobic respiration is lactic acid. This is created because of the build up of unused oxygen and acetyl coA from the krebs cycle. These molecules, along with left over CO2 forms lactic acid which can build up in the cells and produces a burning sensation. The cells then need to work hard to eliminate this lactic acid in order to not shut down.

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Anaerobic activities permits the blood to transport latic acid to the liver, where it is changed back into glucose and brings oxygen back to the muscles.

https://www.sciencedirect.com/topics/medicine-and-dentistry/anaerobic-metabolism#:~:text=Cooling%20down%20after%20hard%2C%20anaerobic,supply%20the%20body%20with%20energy.