Question

During marathon, we sometimes get painful contractions of leg muscles due to the accumulation of one of the following in leg muscles. This is :

• A. carbon dioxide
• B. alcohol
• C. lactic acid
• D. lactose

Answer 1

The correct option is C lactic acid

Correct answer: (d) lactic acid.
During heavy exercise, the demand for energy is high but the supply of oxygen to produce energy is limited. Therefore, anaerobic respiration takes place in the muscle cells to fulfil the demand for energy.
Due to anaerobic respiration, there is an accumulation of lactic acid in muscle cells that leads to painful contractions or cramps in leg muscles.