The most common causes of soreness in the left thigh are over-exercise, soft tissue injury, lumbar disc herniation and so on. 1. Excessive exercise: If the patient is engaged in strenuous sports, it is easy to cause lactic acid to accumulate in the left thigh, and the metabolism of lactic acid may cause the feeling of soreness in the left thigh, which can be relieved after sufficient rest. 2. Soft tissue injury: If the left thigh is traumatized and the local nerves are damaged, it will be easy to have the soreness and numbness of the left thigh. 3. Herniated lumbar intervertebral discs: a herniated lumbar intervertebral disc compressing the nerve root can also cause numbness in the lower limbs, which in turn can cause numbness in the left thigh. Caused by the left thigh sore feeling of more reasons, but also may be related to the pear-shaped muscle syndrome, fasciitis and other reasons, if the symptoms are not relieved after resting, it is recommended to go to the hospital in a timely manner to find out the cause of the disease, by the doctor targeted treatment.