Fast running, taken as an example of exercise is often followed by a high breathing rate, increased heart rate, increased blood pressure and easy muscle fatigues. All other physiological symptoms are due to activation of the sympathetic system in running or any other strenuous exercise, but what about lethargy and muscle cramps that restrict our ability to do continuous work? The chemical to be blamed is lactic acid.

What is lactic acid used for in the body?

Lactic acid is a breakdown product of glycogen, a natural organic compound present in the RBCs, muscles, liver, kidney and other parts of the body. It is an important fuel and provides energy to the body during an-aerobic physical activity.

Depending upon the source of energy and oxygen level in the body, exercises are divided into two types; aerobic and non-aerobic.

Aerobic exercises – are the ones in which there is a sufficient supply of oxygen. Characteristic features of aerobic exercises are:

  • High-intensity activity
  • A normal level of oxygen
  • The main source of energy are carbohydrates (glucose)
  • Glucose is converted into pyruvate
  • No soreness or muscle cramps

An-aerobic exercises – an-aerobic means “with oxygen” i.e. exercises with decreased oxygen supply. Characteristic features are

  • Low-intensity activity
  • Low level of oxygen
  • The main source of energy is stored products e.g. lactic acid
  • Glucose is converted into lactic acid
  • You run out of breath due to exhaustion, fatigue and muscular cramps.

So the questions often asked are, is lactic acid is good or bad? Is it a waste product? What is lactic acid used for in the body? In this article, we discuss lactic acid; its production and why the body uses it.

The real science behind lactic acid

There is a lot of fuss and misconceptions about lactic acid in the “running world”. Until recently, it was assumed that exhaustion, fatigue and soreness during strenuous exercise are due to an accumulation of lactic acid in the muscles. It is the reason why many athletes and sportsmen thought that lactic acid is some sort of waste product or toxin associated with a reduction in their performance. However, recent scientific studies reveal that though lactic acid is associated with fatigue and exhaustion of the body muscles it is not as harmful as many people thought, unlike what is assumed, it is synthesized in the body for an important purpose.

In a normal physical activity or when we start to exercise, we are in the aerobic state and all the body tissues are fully saturated with oxygen. Contraction of muscles needs energy which is supplied by the break down of glucose (glycolysis) into pyruvate in the presence of oxygen.

High effort exercises, on the other hand, require extra energy and oxygen supply to hyper-working muscles (for rapid contraction), to heart (to increase the force of contraction) and to the brain (main control centre). Decrease supply of oxygen by the lungs and depletion of glucose forces the body to shift its metabolism from aerobic state to an-aerobic state. Now the end product of same glycolysis converted to lactic acid instead of pyruvate. This lactic acid is broken down in the muscles due to the presence of an enzyme called lactic acid oxidase and is used as fuel for muscle contraction.

Is lactic acid good or bad?

Lactic acid is highly unstable and readily converted into lactate and hydrogen. Lactate formed this way is now available as a secondary source of energy for the muscles while hydrogen is a strong acid and its accumulation accounts for fatigue, exhaustion and cramps. Cramps are the body’s way of protecting the rapid contracting of muscles because if this phenomenon doesn’t occur it will lead to spastic paralysis of the muscles.