The correct answer is option 1 - Lactic acid. During intense exercise, such as sprinting, the body requires a lot of energy. To meet this energy demand, glucose is broken down through a process called glycolysis, which occurs in the muscles. This process produces a compound called pyruvic acid. However, when the oxygen supply to the muscles is limited, which can happen during high-intensity exercise, pyruvic acid is converted into lactic acid.

Lactic acid is normally cleared from the muscles through the bloodstream and metabolized by the liver. However, during intense exercise, lactic acid can accumulate in the muscles faster than it can be cleared. This build-up of lactic acid in the muscles can lead to discomfort and cramping.

The other options are not directly related to muscle cramps. Ethanol is a type of alcohol that can affect muscle function, but it is not typically associated with cramps. Pyruvic acid is a byproduct of glycolysis, which is converted to lactic acid, but it is not the direct cause of cramping. Glucose is the initial source of energy during exercise, but it does not directly lead to cramps.

Therefore, the correct option is lactic acid as it