context: Muscles exert energy using force. The motion is either exposed or non-internal. There are three types of muscles. The contractions of the heart and bowel muscles are essential for man's survival. Determined muscles are important for man's body movement. One estimate is that there are approximately 639 muscles in our body. The heart and bowel muscles are involuntary muscles that move without our knowledge.
question: How many types of muscles are there in the human body?
answers.text: three