Swelling and hardening of the calves in summer may be caused by physiological reasons, or pathological reasons such as varicose veins of the lower limbs, knee joint lesions, bone tumors and other diseases. 1. Physiological reasons: due to long-distance running, mountain climbing and other strenuous exercise, resulting in the accumulation of lactic acid in the calf muscles, the symptoms of swelling and hardening of the calves may occur. 2. Pathological causes (1) Varicose veins of the lower limbs: As patients suffer from varicose veins of the lower limbs, the symptoms of swollen and hardened calves may occur when blood circulation is obstructed. (2) Knee joint lesions: Knee arthritis and other diseases of the knee joint may lead to symptoms of swelling and stiffness of the calf. (3) Bone tumors: Bone tumors in the calf area may cause swelling and hardening of the calf due to the enlargement of the tumor. There are many reasons for the swelling and hardness of the calf in summer, if it is difficult to relieve, it is recommended to go to the hospital for examination, to clarify the cause of the disease and then follow the doctor’s instructions for treatment.