The pain in the left calf may be caused by the following reasons: 1, lumbar disc protrusion, when the lumbar disc protrusion, can compress the nerve roots and lead to pain in the left lateral calf, accompanied by numbness and weakness of the toes, to CT and nuclear magnetic examination for further diagnosis and treatment. 2, fasciitis, when the outer calf fasciitis, there will be calf pain, can be pain in the back of the calf, often in the cold or tired, walking too much pain. 3, rheumatoid disease, when there is rheumatoid, can appear calf muscle, and fascia pain, can appear obvious fear of cold, fear of wind and other symptoms, this time to carry out laboratory tests to further diagnosis and treatment.