The human body has approximately 650 muscles, which weigh up to half of a person's total weight. Each muscle performs a specific function necessary to the body. Muscles are designed to provide strength and speed, through contraction and expansion, enabling parts of the body to move voluntarily and involuntarily. Every human function is performed with the use of muscles, which are made of fibers that produce movement. They're connected to the bones by tendons, and there are three types of muscles in the body: skeletal, smooth and cardiac.
Skeletal
Skeletal muscles cover the bones, providing shape and definition for the body. These are the muscles most people think of when they tone for strength. Their movement is through voluntary actions, so you're able to control their performance. Skeletal muscles act to help you with posture, keeping the body erect. They also hold the bones together and prevent dislocation of the joints. Even the face has muscles, enabling you to have facial expressions such as smiling, grimacing, frowning or smirking. The two types of contractions the skeletal muscles can perform are brief contractions, also known as twitching, and longer contractions. Skeletal muscles also produce heat, which helps keep body temperature stabilized.
Smooth
Smooth muscles, located throughout the body, help with internal organ activity through involuntary action. They're found in the digestive system, urinary tract and around all the other organs. They are also involved in the airways and lungs. Smooth muscles are responsible for squeezing the uterus during childbirth to push the baby toward the birth canal. The smooth muscle in the eye causes dilation and contraction of the pupil, based on the amount of light. It also controls arterial blood flow. Smooth muscle activity requires no conscious thought.
Cardiac
The cardiac muscle is only in the heart. It does its job routinely and involuntarily. Since it's crucial to life, it never stops functioning. The cardiac muscle performs two functions: squeezing to push the blood from the heart and relaxing so the heart can fill back up with blood. The cardiac muscle can stretch and contract with great force, like that of a skeletal muscle.
