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Muscles get fatigue due to the accumulation of which molecule?
A. Lactic acid
C. Phosphate molecules
D. $C{O_2}$

Last updated date: 17th Jun 2024
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Hint: Muscle fatigue is a medical condition in which there is a decrease in the ability of producing force, feeling of tiredness, lack of energy, etc. If this condition is not recovered on time then it may lead to, chronic fatigue syndrome (CFS), overtraining syndrome, endocrine disorders, immune dysfunction, organic disease, etc.

Complete answer:
For proper functioning of any part of the body, we need energy that is, ATP, proper oxygen concentration and glucose. Which will allow aerobic respiration to occur in presence of glucose and oxygen and will lead to formation of ATP which will help in muscle contraction.
In aerobic respiration, glucose will undergo glycolysis and will convert into pyruvate along with production of ATP molecules in the mitochondria. Here if sufficient oxygen is present then it will undergo Krebs cycle but if oxygen is not sufficient for the process then it will not undergo Krebs cycle instead pyruvate will accumulate in the muscle fibres.
Pyruvate which is accumulated in muscle fibres will get converted into the lactic acid and when a large amount of pyruvate accumulates in the muscle then it will increase the production of lactic acid in the muscles. This large accumulation of lactic acid will reduce the pH and hence acidity will be increased which will lead to stinging feelings in muscles and increase muscle fatigue.

Thus, we can say that muscle fatigue will be induced with the accumulation of lactic acid thus, option ’A’ is the correct answer.

Note: When enough amount of oxygen is present then glucose will undergo aerobic respiration. If the respiratory or circulatory system is not able to fulfil the demand required by the body or muscles, it will undergo anaerobic respiration and will produce energy from that process.