<P> Eccentric contractions normally occur as a braking force in opposition to a concentric contraction to protect joints from damage . During virtually any routine movement, eccentric contractions assist in keeping motions smooth, but can also slow rapid movements such as a punch or throw . Part of training for rapid movements such as pitching during baseball involves reducing eccentric braking allowing a greater power to be developed throughout the movement . </P> <P> Eccentric contractions are being researched for their ability to speed rehabilitation of weak or injured tendons . Achilles tendinitis and patellar tendonitis (also known as jumper's knee or patellar tendonosis) have been shown to benefit from high - load eccentric contractions . </P> <P> In vertebrate animals, there are three types of muscle tissues: skeletal, smooth, and cardiac . Skeletal muscle constitutes the majority of muscle mass in the body and is responsible for locomotor activity . Smooth muscle forms blood vessels, gastrointestinal tract, and other areas in the body that produce sustained contractions . Cardiac muscle make up the heart, which pumps blood . Skeletal and cardiac muscles are called striated muscle because of their striped appearance under a microscope, which is due to the highly organized alternating pattern of A bands and I bands . </P> <P> Excluding reflexes, all skeletal muscles contractions occur as a result of conscious effort originating in the brain . The brain sends electrochemical signals through the nervous system to the motor neuron that innervates several muscle fibers . In the case of some reflexes, the signal to contract can originate in the spinal cord through a feedback loop with the grey matter . Other actions such as locomotion, breathing, and chewing have a reflex aspect to them: the contractions can be initiated both consciously or unconsciously . </P>

Muscles that assist in a movement are called