Hard lumps in calf muscles are considered to be related to physiological causes, muscle spasms, fibromas, muscle injuries, bone tumors, venous thrombosis and so on. 1. Physiological reasons: such as not stretching in time after a lot of exercise, which may lead to muscle hardness. 2. Muscle spasm: lack of calcium or catching a cold can cause calf muscle spasm, localized hard lumps, when the cramps relieve the lumps will generally disappear. 3. Fibroma: generally a round swelling, hard texture, with a certain degree of mobility, benign swelling, through ultrasound can be clearly diagnosed. 4. Muscle injury: when scarring occurs during the healing process of local muscle tissue after muscle injury, there may be hard lumps when touching. 5. Bone tumor: when the tumor invades the surrounding tissues, there may also be hard lumps in the lower leg with small mobility, which can be clearly diagnosed through radiography. 6. Venous thrombosis: thrombosis can lead to swelling in the calf area and hard lumps may also be felt. Hard lumps in the calf muscles need to go to the hospital for examination and clear cause for treatment.