The burning sensation in your quads as you sprint up a hill or the soreness in your biceps as you finish your last rep- we’ve all been told by a coach or friend that “it’s just lactic acid.” But what is it really, and why is it happening?

Lactic acid is a chemical byproduct of anaerobic respiration. Woah woah woah- what does that mean? Essentially, your body creates energy from a process called cellular respiration. The first step is called glycolysis, where glucose is broken down into a molecule called pyruvate (that’s why it’s important for athletes to replenish with lots of carbs- it’s how we get our energy!). The body uses this chemical to create more energy in the presence of oxygen. When the body burns energy aerobically, this means that it is undergoing aerobic respiration. Your body prefers to make energy this way, and it’s what happens throughout most of the day.

What happens differently when you exercise? Notice how you breathe faster when your body is performing strenuous activities- this is an attempt to shuttle more oxygen to working muscles. However, sometimes our bodies require energy production faster than our bodies can deliver oxygen. This is where anaerobic respiration comes in. Because oxygen is in short supply, the body extracts energy from pyruvate by converting it into lactate- otherwise known as lactic acid. This ensures that glucose can still break down and the process of energy production can continue. Lactic acid builds up in tissues and enters the bloodstream, where the body can use small amounts to create energy. The liver breaks down any excess lactate in the blood.

Why doesn’t the body always convert energy this way? Well, muscles can only continue this intense anaerobic activity at high rates for 1-3 minutes. High lactate levels increase the acidity of muscle cells and disrupt other metabolites, and metabolic pathways that break down glucose perform poorly in this environment, causing the body to stop or slow down strenuous activity. This natural defense mechanism prevents permanant damage to the body from extreme exertion. Oxygen becomes available again once the activity is stopped, and the lactate converts back to pyruvate. Aerobic respiration can resume.

Lactic acid buildup in muscles during exercise typically isn’t harmful, and it can actually be beneficial. It helps the body absorb energy and increases endurance levels. However, some people prefer to reduce lactic acid buildup as much as possible. To do so, consider drinking water to break down excess lactic acid, taking deep breaths to help deliver oxygen to muscles, decrease exercise intensity to allow oxygen levels in your blood to recover, and stretch after exercise to help alleviate the burning sensation.

It is worth noting that lactic acid build up does not cause DOMS, delayed onset muscle soreness. This feeling is most likely a result of starting a new type of exercise, changing exercise routines, or increasing the duration or intensity of a regular workout.

Lactic acid production is a natural, and healthy, reaction of your body to produce energy when it has insufficient oxygen. Next time you feel a burning sensation in your muscles while pushing through an intense activity, acknowledge that you are getting stronger and remember to take breaks for your body to recover. Your body can do really cool things.

Works Cited

“How to Get Rid of a Lactic Acid Buildup.” Medical News Today, 2 Oct. 2019, www.medicalnewstoday.com/articles/326521. Accessed 31 May 2021.

Roth, Stephen M. “Why Does Lactic Acid Build up in Muscles? And Why Does It Cause Soreness?” Scientific American, 23 Jan. 2006, www.scientificamerican.com/article/why-does-lactic-acid-buil/. Accessed 31 May 2021.

Whitcomb, Isobel. “What Is Lactic Acid? (And Where Does It Come From?).” Live Science, Future US Inc, 2020, www.livescience.com/lactic-acid.html#:~:text=Lactic%20acid%2C%20or%20lactate%2C%20is,muscle%20and%20red%20blood%20cells. Accessed 31 May 2021.

Notes:

https://www.livescience.com/lactic-acid.html#:~:text=Lactic%20acid%2C%20or%20lactate%2C%20is,muscle%20and%20red%20blood%20cells.

• Lactic acid = chemical byproduct of anarobic respiration

• Anaerobic respiration = the process of cells producing energy without the presence of oxygen

• NOT the cause of muscle soreness after exercise

• Harmless – returns to normal levels at rest

• How it’s produced:

• Body burns energy aerobically (in the presence of oxygen) throughout most of the day through a process called glycolysis

• End product of glycolysis is pyruvate, which is a chemical the body uses to produce more energy

• Energy can only be extracted from pyruvate in the presence of oxygen

• Muscles need more energy as you work harder – when your body is making energy anarobically, energy is not extracted by pyruvate but rather pyruvate gets converted to a waste product and is released into the bloodstream (lactic acid)

• Muscles switch to anaerobic respiration because it’s a much quicker wa to produce energy, especially when you cannot pump oxygen quick enough into your muscles

https://www.scientificamerican.com/article/why-does-lactic-acid-buil/

• Breathe faster when perform strenuous exercise to attempt to shuttle more oxygen to working muscles

• Aerobic respiration preferred, but sometimes our bodies require energy production faster than our bodies can deliver oxygen -> generate energy anaerobically instead

• How lactic acid is produced: Typically, energy comes a process called glycolysis, where glucose is broken down into pyruvate. Pyruvate is further broken down in the presence of oxygen to create more energy, but when oxygen isn’t present, the body temporarily convert pyruvate into lactate so glucose breakdown and the process of energy production can continue.

• High lactate levels in muscles increases the acidity of muscle cells and disrupts other metabolites -> metabolic pathways that breakdown glucose perform poorly in this environment, which causes the body to stop strenuous activity = natural defense mechanism by preventing permanate damage from extreme exertion -> oxygen becomes available once the activity is stopped and the lactate converts back to pyruvate, so aerobic metabolism can again occur

• Muscles can continue this high anaerobic activity at high rates for 1-3 minutes

• Lactic acid buildup is not responsible for muscle soreness following strenuous activity

https://www.medicalnewstoday.com/articles/326521

• Oxygen in the blood needed to convert gluscose to energy, but when there is insufficient oxygen, the body breaks down glucose a different way, resulting in lactic acid

• Lactic acid builds up in tissues and enters the bloodstream, where the body can use small amounts to create energy

• Lactic acid buildup is commonly induced by strenuous exercise

• Liver will break down any excess lactate in the blood

• Lactic acid buildup in the muscles during exercise isn’t harmful, and a little can be beneficial: helps the body absorb energy, increases endurance levels

• To prevent lactic acid buildup:

• Drink water – breaks down excess lactic acid

• Take deep breaths – helps deliver oxygen to muscles, slowing the production of lactic acid

• Decrease exercise intensity – allows oxygen levels in blood to recover

• Stretching after – helps alleviate burning sensation that lactic acid can cause

• Lactic acid buildup does not cause DOMS, delayed onset muscle soreness

• More likely a result of starting a new type of exercise, changing exercise routines, or increasing the duration or intensity of a regular workout