The pain in the left inner calf muscle may be caused by muscle strain, myofasciitis and lumbar disc herniation. 1. Muscle strain: commonly seen in patients who engage in strenuous exercise and heavy physical activities, when the patient’s left inner calf muscle strain, usually manifested as severe pain in the inner side of the left calf and other symptoms. 2. Myofasciitis: If the patient’s inner left calf has been traumatized or has repeated strain injury, myofasciitis may be induced, which may lead to the occurrence of pain in the inner tendon of the left calf. 3. Lumbar disc herniation: in some patients with lumbar disc herniation, when the herniated disc compresses the central nervous system, it may also cause the symptom of left medial calf tendon pain. Therefore, if the patient has severe or persistent left medial calf tendon pain, he or she should go to the hospital in time for treatment.