In ascending order of severity, a muscle may be affected by a contracture, stretch, or tear.
In the former the muscle tissue contracts, in the latter it is overstretched, and in the tear there is a rupture of muscle fibers: this may be a partial rupture of a few fibers or a total rupture of a muscle, which is normally injured at a point of greatest weakness, at the junction of bone and tendon or where it has previously suffered trauma.
Strains and tears can affect any muscle, but they are especially common in the lower back, neck, shoulder, and tendon of the knee.
