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What is lactic acid?

Hadyn Luke posted this on Friday 28th of December 2012 Hadyn Luke 28/12/2012

Tags: Anatomy and physiology

lactic acid

Our fitness blog this week looks at lactic acid – what it is and its effect on exercise and training, which is useful to know for anyone working as a personal trainer or fitness instructor.

As anyone following a health and fitness course will learn during training, lactic acid is a by-product of glycolyisis- the breaking down of sugar. It is constantly produced by the body as we respire and break down sugars and fats. During aerobic respiration, we use sugars and fats to create energy – in fact, there’s a saying that fat burns in the flame of sugar. Even when we are at rest, we are still synthesising a small amount of sugar, and as lactic acid is a by-product of this, it is always present in our bodies. However, since energy expenditure is relativley low our bodies can remove the lactic acid faster than it is produced and it is not an issue.

Why lactic acid is produced

As we increase the intensity of our activities, whether in normal daily life or working with a personal trainer at the gym, we recruit more aerobic energy from our aerobic pathways, and therefore start to oxidize more fat and more sugar, which leads us to produce more lactic acid. Eventually, if intensity continues to increase, the rate of production may become greater than our abilitiy to remove it.

Contrary to popular belief, it’s not lactic acid itself that is detrimental to exercise. When a person is primarily exercising aerobically, at a low to medium intensity, the lactic acid in their body gets turned into pyruvate, which enters the aerobic system. In this instance, there aren’t any other by-products created.

The cause of muscle burn

However, if you are working with a personal trainer and the intensity of your exercise is increased, there will be less oxygen available and you will start to recruit more sugars from your anaerobic system. At this point, the lactic acid cannot be synthesised as pyruvate and turns into pyruvic acid and produces a hydrogen ion as a by-product. It is this hydrogen ion that makes your muscles feel as if they are burning, as hydrogen changes the ph within the internal environment of the muscle so that it turns more acidic. At this point, you are likely to stop training because of muscle burn.

Why lactic acid has a bad name

When an individual is training hard at a fitness class or with their personal trainer, and their muscles feel as if they are starting to burn, lactic acid tends to get the blame. The reason for this is that for every molecule of lactic acid that the body produces, it also produces a molecule of hydrogen ion. As hydrogen ions are difficult to monitor, a fitness instructor will monitor a client’s lactic acid instead – hence it getting a bad name. In fact, it is the hydrogen ions that are to blame.

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