The pronator quadratus muscle is a small, square-shaped muscle located in the forearm. It originates at the lower end of the ulna (one of the two bones in the forearm) and inserts into the distal aspect of the radius (the other bone in the forearm). The pronator quadratus muscle is located deep to the pronator teres muscle, and is one of several muscles that make up the posterior compartment of the forearm.

The main function of the pronator quadratus muscle is to pronate (rotate downwards) the hand and wrist. This movement allows the palm of the hand to face downwards, and is essential for activities such as turning a doorknob or holding a pencil. The pronator quadratus muscle also helps to stabilize the elbow joint and assist in the fine movements of the fingers.

In sports, the pronator quadratus muscle may be used in activities that involve gripping or throwing objects, such as tennis, golf, and baseball. It may also be used in activities that require fine control of the fingers, such as playing the piano or guitar.

In everyday life, the pronator quadratus muscle is used in many activities that involve gripping or holding objects, such as opening a jar, turning a doorknob, or writing with a pen or pencil. It is also used in activities that require fine control of the fingers, such as buttoning a shirt or tying shoelaces.