Whereas the larger exterior muscles of the arm provide the most profound movements, such as the bending of the elbow and wrist, the smaller deep muscles of the arm perform many functions, such as twisting the wrist or moving the fingers. It is because of these muscles that the wrist and fingers can perform such detailed tasks.

Some deep muscles of the arm include:

  • Flexor digitorum profundus: This long forearm muscle flexes the hand and fingers.
  • Extensor pollicis brevis: Another important thumb muscle, this one acts in conjunction with the abductor pollicis longus to extend and bend the thumb outward.
  • Supinator: This muscle near the elbow helps the bicep muscle to turn the hand palm-side up.
  • Pronator quadratus: This quadrangle-shaped muscle is attached to both the radius and the ulna, and its job is to rotate the forearm and wrist as well as keep the proper distance between the radius and ulna.

Because the deep muscles of the arm perform such small and specialized functions that play a huge role in daily tasks, they are prone to injury. Problems with these muscles and their associated tendons can limit a person’s joint dexterity as well as cause pain and irritation.

Repetitive stress injuries, due to activities such as playing sports or using a keyboard, can cause inflammation and pain. Collectively, these injuries are known as tendonitis. If the tendon on the outside of the joint is affected, it is called “tennis elbow.” If it is the tendon on the inside of the elbow, the condition is known as “golfer’s elbow.”