Weakness and tenderness of the thighs may be due to physiological factors, but also may be related to lumbar disc herniation, femoral head necrosis and other diseases. 1. Physiological factors: If you perform strenuous exercise within a short period of time, it is easy to cause local muscle injury or lactic acid buildup, which will lead to weakness and tenderness of the thighs. 2. Lumbar disc herniation: the herniated lumbar disc compresses the local nerve root, which may cause weakness and tenderness of the thighs, as well as lumbar pain, leg numbness, leg pain and other symptoms. 3. Necrosis of the femoral head: Necrosis of the femoral head can easily cause atrophy of the thigh muscles, resulting in weakness and tenderness of the thighs. Thigh weakness may also be related to spinal cord compression, knee osteoarthritis, lumbar spinal stenosis and other diseases, it is recommended to go to a regular hospital in time, under the guidance of the doctor to standardize the treatment, so as not to delay the condition.