"A muscle gets injured when it is taken forcibly beyond it's threshold for elasticity. You see muscle is like a telescoping sausage. First, muscles are like sausages because each muscle group has a casing, which they call the fascia, much like the skin of your favorite deli sausage, it allows for the muscle to move within it's specified boundaries while decreasing the chances of the muscles tearing. So in a way this fascia is crucial the the strength of a muscle group while keeping them organized for a specific use "