Final answer:
Lactic acid fermentation causes muscle cramps in animal skeletal muscles when oxygen supply is insufficient. It converts pyruvate into lactic acid and produces ATP for energy. Recent research disputes the belief that lactic acid accumulation causes muscle stiffness, fatigue, and soreness.
Step-by-step explanation:
The fermentation method that causes muscle cramps is lactic acid fermentation. This type of fermentation occurs in animal skeletal muscles when there is an insufficient oxygen supply to allow aerobic respiration to continue. In lactic acid fermentation, pyruvate is converted into lactic acid, and this process produces ATP to provide energy to the muscles. The accumulation of lactic acid in the muscles was once believed to cause muscle stiffness, fatigue, and soreness, although recent research disputes this hypothesis.