Their function of muscles is to produce force and cause motion. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Examples are the contraction of the heart and peristalsis which pushes food through the digestive system.

Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh. There are two broad types of voluntary muscle fibers: slow twitch and fast twitch.

Slow twitch fibers contract for long periods of time but with little force while fast twitch fibers contract quickly and powerfully but fatigue very rapidly. the muscle also helps us to have enough energy and more strength if we are sick the muscle still trys to hold in all the sick cells together and have them gave us more energy to stand or run .

The movement of skeletal muscle is the result of muscle that work in pairs. If a bundle of muscles contract, the muscles become shorter, harder and larger in diameter. When a bundle of muscles relax, then they become longer, softer and smaller in diameter.

Muscles consume energy. Muscle uses chemical energy in the from of glucose. When the glucose is broken down, the chemical energy transforms into mechanical energy, than the muscles contract. When the supplied glucose in the muscles finally runs out, muscles become tired.

Muscles also produce heat energy during contraction. The heat produced by muscle contraction helps to maintain your body temperature constant.

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