Sudden thigh cramps are caused by the dysfunction of the muscles and nerves, and the muscles experience involuntary and continuous spasmodic contractions, resulting in cramping symptoms. Common causes include the following: a. Acute injury and chronic strain on the thigh muscles. Acute injury can lead to muscle congestion, edema, and in severe cases, bleeding, which affects the function of the muscle and causes involuntary spasmodic contraction. Chronic strain injury can be due to the stimulation of local inflammation, but also may be due to excessive exercise, resulting in the accumulation of metabolites within the muscle stimulation, the emergence of muscle dysfunction, resulting in cramps. Second, calcium deficiency, calcium ion is an important ion for muscle function to achieve, when calcium ion deficiency, the muscle will also appear corresponding functional abnormalities, resulting in involuntary, persistent contraction spasm. Third, nerve diseases, including lumbar spine slippage, lumbar disc herniation, etc., the sciatic nerve root in the lower limbs is compressed leading to abnormal nerve function and abnormal discharge, which will also lead to abnormal muscle function, abnormal contraction and spasm.