In part one we discussed the throwing anatomy of the shoulder and upper torso muscles that are chiefly involved in throwing.  All of those muscles transmit their power down the upper arm, forearm, and finally the fingers, which release the ball. Today we will discuss the upper arm and forearm compartment muscles.

Accelerators

Triceps Brachii

The triceps is another muscle not known for its role in throwing, but it performs a crucial task: straightening the arm before release.  The triceps originates in three places (triceps means “three heads”): the scapula, and two different points on the posterior humerus. It inserts on the olecranon process (funny bone) of the ulna.

A very tiny muscle called the anconeus, which connects the humerus to the ulna, also assists the triceps in the extending the arm.

The triceps acts to extend the arm before release.

Forearm Pronators

Arm fully pronated after release

Pronation (turning your palm down and inward) naturally occurs during throwing, regardless of the pitch thrown. The muscles responsible for this action are located in the anterior compartment of your forearm and are referred to as (you guessed it!) pronators.

Pronator Quadratus

Pronator quadratus, which originates on the anterior ulna and inserts near the wrist on the radius, is the prime mover of forearm pronation.  Having strong pronators is crucial to keeping your elbow healthy and happy, and can help you get more movement on the ball.

Pronator Teres

Pronator teres is two-headed and originates on the ulna and humerus.  Its insertion is midway down the radius on the lateral aspect.  This is the second of two dedicated pronation muscles.  

Hand and Wrist Flexors

I’m grouping these together because there are a bunch of these, all acting in concert.  There are 5 flexors acting on the fingers, and one more that acts on the thumb (flexor pollicis longus).

The prime movers of the group are the flexor carpi radialis, the flexor carpi ulnaris, and the flexor digitorum superficialis.  The other two synergists are the flexor digitorum profundus and the palmaris longus.

Why the long names, you ask?  Well, they tell you what each muscle does, silly!

Flexor = decreases angle at a joint

Carpi = acts on the wrist ; digitorum = acts on fingers ; pollicis = acts on thumb

Ulnaris = along the ulna ; radialis = along the radius ; superficialis = toward the surface

So put them together, and each name tells you the action of the muscle, on which body part it acts, and where it is located.  Easy, right?

The anterior forearm compartment, containing the flexors

If the palmaris longus sounds familiar (the muscle with the long tendon that acts on the palm) it is because surgeons typically use a piece of the tendon as the graft for Tommy John Surgery.  It’s a very weak flexor, anyway.

The forearm flexors are crucially important, as they stabilize the elbow joint and add that last bit of oomph to the baseball.  When the flexors fire, the hand releases the ball and follows through.  It’s a waste of perfectly good mphs to see a pitcher with scrawny and weak forearms.

Try to flex just your ring finger.  Can’t do it?  That’s because your fingers are controlled jointly by the same flexor muscles.  The body is quirky like that.

The Decelerators

Biceps Brachii

The biceps is overlooked for two reasons: It helps to slow the arm after release, and one of its tendons is a major shoulder stabilizer.  Let me explain:

The biceps (meaning two heads) originates in two important places: the coracoid process, which is a bony protrusion on the anterior scapula, and the glenoid (shoulder) cavity.  The biceps tendon goes through the capsule and attaches to the labrum. The labrum helps deepen the shoulder cavity, which provides additional stability for the joint. Strong biceps = strong force holding the humerus in the shoulder socket.

Now, jacking up your biceps isn’t going to magically keep your shoulder healthy, and that’s not what I am suggesting.  I AM suggesting that having good bicep strength, along with the rest of the shoulder stabilizers, is important to keeping an optimally stable shoulder, which helps ward of throwing injuries.  If your shoulder is firmly held in proper position by strong muscles, then things that shouldn’t move won’t, and everything can work as it is supposed to.

After a pitch is released, the biceps have to contract to start controlling the movement as the arm extends and travels forward.  The bicep is also a forearm supinator, which counteracts the pronation of the arm after release.  Pitchers that open their hips up too early often complain of bicep fatigue, which is likely a product of it becoming active as the arm is still accelerating.

Brachialis

Residing underneath and assisting the biceps brachii, the brachialis flexes the elbow and attempts to slow the arm down, opposing the action of the triceps after release.

Brachioradialis

A semipronator and semisupinator, depending on arm orientation, the brachioradialis inserts on the radius close to the wrist and originates on the humerus close to the elbow.  This muscle aids in elbow flexion, and may provide assistance in slow the arm and hand after release.

The Supinator

Yep, the only dedicated supination (moving your thumb laterally and your palm to the sky) muscle is called the supinator.  It acts alone during slow supination, but is assisted by the biceps otherwise.  To counteract the pronation of the arm after release, this bad boy is firing hard.

Wrist and Hand Extensors

These muscles occupy the posterior compartment of the forearm, and act to bring the hand back, as in giving someone the “STOP” gesture.

Before the ball is released, these muscles act to lay the hand back, so that maximum range of motion may be achieved when the flexors contract.  After the ball is released, these muscles activate to slow the hand back down.

The forearm extensors

The extensor group is named just as the flexors are, so you can probably figure out exactly where they are and what they do.  The prime mover is the extensor digitorum; other synergists are the carpi radialis, brevis and longus, extensor carpi ulnaris, extensor pollicis longus and brevis, and extensor indicis. Mouthful.

But strengthening the extensors are just as important as the flexors, because muscle balance is important to staying injury free – ask any serious rock climber.

Rock climbing is hours upon hours of extremely strenuous finger and wrist flexion under a heavy load, which, if not balanced out with proper extensor strengthening, leads to tears, tendinitis, carpal tunnel and more.  The body loves balance.

Wrap-Up

Take care of your lower arms, and don’t forget your beach muscles, even if you’re a pitcher.  Size with mobility is ideal, but it’s not always about being big.  Being strong all over is crucial to performing at your best.

Critical areas on the throwing arm are the shoulder and forearm, but hopefully this anatomy lesson is leading you to realize that the body works as a whole, and training should reflect that while paying special attention to the muscles that are overly involved in the throwing motion.

Part 3 and part 4 are going to get complicated, as they will involve the lower extremities and core muscles, of which there are lots, doing lots of different things. Stay tuned…