Why do you feel tired when exercising - Lets go medical

Lactic Acidosis is a form of Metabolic Acidosis that forms in the body when lactic acid production increases or decreases and the body cannot cope with these changes.

Cells get the energy needed from the Glucose reaction, but when a person runs quickly, another reaction takes place in the cells called Anaerobic Respiration, where this reaction leads to the transport of glucose into the cells of the body without oxygen, and thus the cells release the remnants of their food in the form of Lactic acid Acid is expressed in the chemical formula C₃H₆O₃.

Lactic acid can form in the mouth due to a special type of bacteria that turns glucose and some types of sugars in the mouth into lactic acid, which in turn causes cavities.

We all notice that after a quick run we keep breathing for some time, in fact the cells use this oxygen to burn lactic acid as it burns with oxygen and dissolves for carbon dioxide and water, and thus does not accumulate in the cells. 2
Types of lactic acid

Class A lactic acid: This class is produced from lactic acid due to a lack of blood flow in the tissues, due to poor cardiac function, sepsis, or cardiac pulmonary stroke.
Class B milk acid: As Class B milk acid results from poor cell performance in some localized regions. 3

Causes of accumulation of milk acid in the muscles

As we mentioned, intense exercise or fast running pushes cells to obtain energy from anaerobic reaction, and thus forms lactic acid as a substance resulting from these reactions in addition to energy, of course.

But if the cells of the body cannot burn the acid with the use of breathing oxygen, it begins to accumulate in the bloodstream, where the speed of its formation is greater than the speed of its burning. This stage is called the Lactate Threshold.

Image Source