What is the substance that causes fatigue in our legs when we exercise too much​

Answer:

The substance that causes fatigue in our legs when we exercise too much is LACTIC ACID.

Detailed Discussion:

When we exercise , the MUSCLE cells initially undergo aerobic glycolysis and obtain large amount of energy from Kreb's CYCLE and Electron Transport chain.

So, initially the muscles receive adequate amount of energy to function.

However , after excessive strenuous exercise , the OXYGEN content in our body decreases (as oxygen intake becomes lesser than utilisation).

So, the glucose in the cells have to undergo PARTIAL oxidation through anaerobic glycolysis to produce pyruvate, which generates SMALL amount of energy through formation of Lactic acid.

This lactic acid accumulates in the muscles and causes fatigue , cramps , etc.

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