Soreness in one leg and nothing in the other may be caused by fasciitis, lumbar spine disease, vascular disease, sports strains and other reasons. 1. Fasciitis: If one leg suffers from fasciitis, under the stimulation of inflammation, the symptoms of soreness will appear. 2. Lumbar spine disease: If lumbar spine disease such as lumbar disc herniation compresses the nerve root, the phenomenon of unilateral leg soreness may occur. 3. Vascular diseases: If you suffer from varicose veins and other vascular diseases that affect the blood circulation of the lower limbs, you may experience symptoms of soreness in one leg. 4. Exercise strain: If muscle strain occurs during exercise, it can lead to local tissue damage and pain symptoms. It is recommended that people with one leg pain and the other one is fine should go to the regular hospital in time to clarify the cause, and if treatment is needed, standardized treatment should be carried out under the guidance of the doctor to avoid delaying the condition.