Question

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

Answer 1

"lactic acid".

hope it helps

Answer 2

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.

$\star$ Hope It Helps.