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  • Writer's pictureJackie Windham



Lactic acid is a by-product of glycolysis, one of the metabolic processes the body uses to produce energy during intense exercise. Lactic acid is the collective term used to describe the lactate and hydrogen ions that are by-products of this process.


Lactic acid is formed within the muscle cells during glycolysis to clear the cells of accumulating pyruvate, a by-product of glycolysis. While still in the muscle cells, the hydrogen ion is what is responsible for lowering the pH of the muscle tissue, making it more acidic. This decrease in the muscle pH, known as acidosis, can lead to some of the burning sensations felt in the muscles during intense exercise. Hence, lactic acid’s a bad rap. The good news, however, is that lactic acid is more of a helper to our muscles since it ultimately provides energy. Here’s how: The lactic acid that is produced during glycolysis is easily disassociated, which means that once lactic acid leaves the muscle cell and enters the bloodstream.

The lactate and hydrogen ion are no longer attached and present as lactic acid, but they are both present separately in the body as lactate and a hydrogen ion. The lactate is often recycled and used as energy, which is much needed during bouts of intense exercise.


Lactic acid is produced during bouts of high-intensity exercise as your body works hard to produce the energy that it needs to sustain the activity. Our bodies use adenosine triphosphate (ATP) as a primary energy source.

Three main energy pathways produce ATP in the body:

  1. The ATP-PC system

  2. The Glycolytic system (glycolysis)

  3. The Oxidative system.

During bouts of high-intensity exercise, like sprints or heavy loads during lifting, the body relies on the ATP-PC and Glycolytic systems (glycolysis) for quick energy because they produce ATP at faster rates than the Oxidative system.

The body will use the ATP-PC system first because it produces ATP the quickest. Once energy resources from the ATP-PC system start to run low, the body turns to the Glycolytic system, or glycolysis, next.

During the process of glycolysis, pyruvate is produced as a by-product. When there’s plenty of oxygen available in the cells, the pyruvate is broken down and turned into more ATP to be used as energy.

However, when a person is performing high-intensity exercise, likely, their body can’t supply oxygen to the cells at a fast enough rate, creating what’s called an anaerobic environment in the cell (anaerobic = without oxygen). When this happens, pyruvate accumulates in the muscle cell, and is quickly converted into lactate, while also releasing a free hydrogen ion in the process.

To clear this traffic jam and resume energy production, the lactate and hydrogen ion pair together as lactic acid so that they can then be removed from the cell and into the blood. In short: lactic acid is formed when the muscle cells don’t have enough oxygen to use their other energy sources.

Once the lactic acid is removed from the muscle cell, it disassociates, and the lactate and hydrogen ion exist separately in the blood. It’s not exactly the lactic acid that builds up in the muscles creating an issue, but rather, there’s an accumulation of hydrogen ions and lactate in the blood that can ultimately impact performance. An excess of these components in the blood could result in acidic conditions that would be damaging to other structures in the body. Fortunately, the body has several ways to deal with the overflow of lactate and hydrogen ions that are released into the blood during intense exercise.


Under normal circumstances, i.e., at rest or during steady-state exercise, the body can manage the excess lactate in the blood by converting it back to energy in a process called the Cori Cycle. To regulate the excess hydrogen ions in the body, the blood contains several buffers to help normalize the pH level that is threatened by the hydrogen ion’s acidity. Thankfully, the lactic acid buildup is not something that we need to be concerned with. There’s no need to shake it out or remove it using external means. The human body is well-equipped to manage this metabolic by-product as it enters the bloodstream. Let’s say you’re going all-out in a workout and the amount of lactate and hydrogen ions in the blood increase at such a rate that the body can’t clear them fast enough. At this point, the ability to exercise at this intensity will greatly diminish…fast. It’s your body’s backup system to prevent a dangerous imbalance internally. There’s no amount of “mind over matter” that can keep you going when your body reaches this physiological state. You’ll be forced to take a break until your body gets back to homeostasis.


The way to reduce the production of lactic acid is to increase your physical fitness so that it takes longer for your body to get to that point. If you’ve ever done high-intensity interval training, you know that when you first start, you tire quickly. Over time, and with proper progression and consistent training, you find that your stamina has increased, and you can train harder for longer periods. Internally what happens is that your body can continue to produce the energy that you need for longer periods before oxygen is no longer sufficiently supplied to the cells and lactic acid is formed.


Lactic acid is the joining of lactate with a hydrogen ion. It’s the hydrogen ion in the lactic acid that contributes to the burning sensation in the muscles during exercise, not the lactate. Lactate, it turns out, helps us out by getting recycled back into our system to provide energy for our muscles! Lactic acid and lactate are sometimes used interchangeably even though they are technically different.


Lactic acid is removed quickly once you lower the intensity of what you’re doing. As a rule for exercise: the more intense the exercise is, the more recovery time you will need. Using strength training as an example, a set of 15 squats using a pair of 15-pound dumbbells will require less recovery time than the same person doing a set of 5 squats using a pair of 60-pound dumbbells. The same goes for cardio: if you do a maximum speed sprint for 20 seconds, you’re going to need more recovery than you would after going for 1 minute at a moderate pace. See Active Recovery Workouts for some great ideas on how to break up lactic acid.

CREDITS TO THE AUTHOR KINSEY MAHAFFEY Kinsey Mahaffey, MPH, is a Houston-based fitness educator, personal trainer and health coach who developed her commitment to lifelong fitness while playing Division I volleyball. She’s passionate about helping others cultivate a healthy lifestyle and enjoys educating other fitness professionals who share this vision. She’s a Master Instructor and Master Trainer for NASM.

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