This released energy is converted into mechanical energy (movement) and heat energy as the muscle contracts (warmth). The thermal energy of muscle contractions aids in the regulation of your body temperature. Muscle activity also increases blood flow to warm-up areas such as the hands, feet, and neck. When you are cold, your body's response is to try to keep itself warm. One way it does this is by reducing the amount of energy it uses at any one time -- which means that more needs to be supplied to it to maintain a constant temperature. So muscles play an important role in keeping us warm too. When we move our muscles they create little bursts of heat, which is why doing some gentle exercise after eating has been found to help reduce appetite. The two main types of muscle are skeletal muscle and smooth muscle. Skeletal muscle is the kind that moves bones or provides force such as in the chest muscles or the leg muscles. It is also responsible for contraction and relaxation of the digestive system. Smooth muscle is the kind that surrounds organs such as the uterus, stomach, and intestines. It helps control the movement of food through the digestive system and plays a role in regulating pressure within these organs. Smooth muscle can be further divided into involuntary and voluntary muscles. Involuntary muscles are those that control functions such as breathing and digestion.