Posterior thigh cramps may be caused by sprains, muscle fatigue, calcium deficiency and herniated discs. 1. Sprains: muscle sprains, hip joint contusion, synovitis, iliotibial bundle and joint capsule injuries can occur in this area, which can cause localized pain and irritate the nerves causing cramps, and in severe cases, can lead to fluid accumulation and activity limitation. 2. Muscle fatigue: after overwork, such as prolonged high-intensity physical exercise and heavy physical labor, resulting in local muscle fatigue, a large amount of lactic acid accumulates in the thigh muscle tissue, which may induce cramps on the back side of the thigh. 3. Calcium deficiency: If there is insufficient calcium in the body, the concentration of calcium ions in the blood will be very low, and the muscles will easily become excited. In the process of contraction, cramps may occur. 4. Herniated disc: When a herniated lumbar disc compresses the nerve root, it will lead to sciatic nerve irritation and may cause cramps on the back of the thigh. If the symptoms of cramps on the back side of the thigh occur frequently and without obvious triggers, you should have a timely medical checkup.