The muscular system plays a very important role in the daily life of an organism. Not only do muscles help with movement, they also help maintain posture, circulate blood, and move substances throughout the body. Additionally, there are three different types of muscles: smooth, skeletal, and cardiac muscles. Skeletal muscle is responsible for a person's movement and behavior, such as walking, running, kicking, or throwing a ball. Most skeletal muscles are attached to bones via tendons. Since one consciously controls the contraction of muscles, the contraction is considered voluntary (Allen and Harper 2013). Smooth muscles are found in blood vessels, the digestive tract, the bladder, and other hollow organs. They propel things through the body, for example, food into the stomach and urine into the bladder. Smooth muscles are considered involuntary and also contract in response to neural stimuli. The third type of muscle is cardiac. Cardiac muscles are found in the walls of the heart. This type of muscle is responsible for pumping the heart so that blood can circulate throughout the body. Additionally, skeletal muscles are surrounded by sarcomeres consisting of thick and thin filaments called myofilaments (Cooper 2000). The thick filaments are made of myosin. On the other hand, thin filaments are made of actin, tropomyosin, and troponin. Actin and myosin are often called contractile proteins (Cooper 2000). When these two substances interact with each other, it causes muscle shortening (Allen and Harper 2013). Muscle contraction occurs when myosin heads interact with thin filaments forming cross-bridges (Sheir, Butler and Lewis 2004). This process begins when the brain sends a signal that releases calcium. Calcium is a fundamental substance that must be present for muscle contraction to occur. It exposes actin binding sites by interacting with tropomyosin (Sheir, Butler and Lewis