Coaching Baseball Pitchers
By Michael G. Marshall, Ph.D.
Copyright 2007
Chapter Sixteen: Forearm Joint
1. Forearm Joint Bones
a. Radius bone
In the forearm joint, the movement of the Radius bone is the forearm joint bone of interest.
The Annular Ligament wraps around the anterior surface of the head of the Radius bone. As a result, the head of the Radius bone does not articulate with the Capitulum on the distal end of the Humerus bone.
Radial collateral ligaments secure the head of the Radius bone to the lateral side of the Humerus bone.
The Radial Tuberosity medially protrudes from the proximal end of the Radius bone just below the head of the Radius bone.
Proximally, oblique cords attach the Radius bone to the Ulna bone. All along the distal two-thirds of the Radius bone, Interosseous membranes attach the Radius bone to the Ulna bone.
The Radius bone rotates toward and away from the non-rotating Ulna bone. Therefore, forearm joint actions only include whether the Radius bone rotates toward or away from the Ulna bone.
1) Anterior Surface
The anterior surface of the Radius bone has two bony landmarks.
01. The head of the Radius bone lies at the proximal (elbow) end of the Radius bone and loosely articulates with the Capitulum of the Humerus bone.
02. From just below the head of the Radius bone, the Radial Tuberosity protrudes medially from the shaft of the Radius bone.
The anterior surface of the Radius bone has two tendon attachments.
01. The two heads of the Biceps Brachii muscle combine into a common tendon that attaches to the Radial Tuberosity of the shaft of the Radius bone.
02. The tendon of the Pronator Quadratus muscle attaches to the anterior surface f the distal one-fifth of the Radius bone.
The anterior surface of the Radius bone has no areas from which muscles arise.
2) Posterior Surface
The posterior surface of the Radius bone has no bony landmarks.
The posterior surface of the Radius bone has, share three tendon attachments laterally with anterior surfaces.
01. The tendon of the Supinator muscle attaches to the proximal one-quarter of the lateral side of the posterior surface of the Radius bone.
02. The tendon of the Pronator Teres muscle attaches to the mid-shaft of the lateral side of the posterior surface of the Radius bone.
03. The tendon of the Brachioradialis muscle attaches to the lateral side of the posterior surface of the distal end of the Radius bone.
The posterior surface of the Radius bone has and no areas from which muscles arise.
b. Ulna Bone
With regard to the actions of the forearm joint, the Ulna bone does not move. This means that, with regard to the forearm joint, we consider the Ulna bone as completely stationary. The Ulna bone only moves with regard to the elbow joint.
1) Anterior Surface
The anterior surface of the Ulna bone has two bony landmarks.
01. The Coronoid Process anteriorly protrudes from the proximal (elbow) end of the Ulna bone.
02. The Styloid Process posteriorly protrudes from the distal (wrist) end of the Ulna bone.
The anterior surface of the Ulna bone has one tendon attachment.
01. The tendon of the Brachialis muscle attaches to Coronoid Process of the Ulna bone.
The anterior surface of the Ulna bone has two areas from which primary pitching muscles arise.
01. Flexor Digitorum Profundus muscle arises from the proximal two-thirds of the Ulna bone.
02. The Pronator Quadratus muscle arises from lines on the distal one-quarter of the Ulna bone.
2) Posterior Surface
The posterior surface of the Ulna bone has one bony landmark.
01. The Olecranon Process lies at the proximal (elbow) end of the Ulna bone.
The posterior surface of the Ulna bone has two tendon attachments.
01. The three heads of the Triceps Brachii muscle form a common tendon that attaches to the Olecranon Process of the Ulna bone.
02. The tendon of the Anconeus muscle attaches to the proximal one-fifth of the Ulna bone.
The posterior surface of the Ulna bone has and one area from which a muscle arises.
01. The Supinator muscle arises from the medial surfaces of the proximal end of the Ulna bone.
2. Forearm Joint Kinesiological Actions
The movement of the Radius bone relative to the fixed Ulna bone defines the kinesiological actions of the forearm joint. The Radius bone either rotates toward the Ulna bone or rotates away from the Ulna bone.
1. Forearm Joint Pronation: When muscles contract that rotate the Radius bone toward the Ulna bone.
2. Forearm Joint Supination: When muscles contract that rotate the Radius bone away from the Ulna bone.
3. Forearm Joint Muscles
At one end, forearm joint muscles attach to the Radius bone. At the other end, they can attach to the Scapula bone, the Humerus bone or the Ulna bone.
a. Biceps Brachii
The two tendons of the Biceps Brachii muscle form a common tendon that attaches to the Radial tuberosity of the Radius bone and to the supraglenoid fossa and coracoid process of the Scapula bone. Therefore, when the Biceps Brachii muscle contracts, these structures move closer together. This means that the Biceps Brachii muscle flexes the Shoulder Joint, indirectly flexes the Elbow Joint and supinates the Forearm Joint.
Because, during the deceleration phase of the baseball pitching motion, baseball pitchers must prevent the olecranon process of their Ulna bone from slamming into its olecranon fossa, after the Triceps Brachii muscle stops extending the pitching elbow, the Biceps Brachii muscle flexes the Ulna bone.
b. Brachioradialis
The tendon of the Brachioradialis muscle attaches to the lateral side of the Radial Styloid process of the Radius bone and to the lateral supracondylar ridge of the Humerus bone. Therefore, when the Brachioradialis muscle contracts, these structures moves closer together. This means that the Brachioradialis muscle flexes the Elbow Joint and supinates the Forearm Joint.
Because, during the deceleration phase of the baseball pitching motion, baseball pitchers must safely return the pitching forearm to its normal resting position, the Brachioradialis muscle supinates the Radius bone.
Because, during the deceleration phase of the baseball pitching motion, baseball pitchers must prevent the olecranon process of their Ulna bone from slamming into its olecranon fossa, after the Triceps Brachii muscle stops extending the pitching elbow, the Brachioradialis muscle indirectly flexes the Ulna bone.
c. Pronator Quadratus
The Pronator Quadratus muscle attaches to the distal one-fourth of the lateral side of the posterior surface of the Radius bone and to distal one-fourth of the lateral side of the posterior surface of the Ulna bone. Therefore, when the Pronator Quadratus muscle contracts, these structures move closer together. This means that the Pronator Quadratus muscle flexes pronates the Forearm Joint.
Because, during the acceleration phase of the baseball pitching motion, baseball pitchers must powerfully pronate the forearm joint, the Pronator Quadratus muscle pronates the Radius bone.
d. Pronator Teres
The Pronator Teres muscle attaches to the lateral surface of the middle one-third of the Radius bone and to the supracondylar ridge of the Humerus bone. Therefore, when the Pronator Teres muscle contracts, these structures move closer together. This means that the Pronator Teres muscle flexes the Elbow Joint and pronates the Forearm Joint.
Because, during the acceleration phase of the baseball pitching motion, baseball pitchers must powerfully pronate the forearm joint, the Pronator Teres muscle pronates the Radius bone.
Because, during the deceleration phase of the baseball pitching motion, baseball pitchers must prevent the olecranon process of their Ulna bone from slamming into its olecranon fossa, after the Triceps Brachii muscle stops extending the pitching elbow, the Pronator Teres muscle flexes the Ulna bone.
During the 1974 National League championship season, Los Angeles Dodger pitcher Tommy John suffered a severe pitching elbow injury. To promote sweating, Tommy wore a rubber jogging jacket. I arrived at Dodger Stadium early two weeks prior to Tommy’s injury and saw Tommy jogging in his rubber jacket. I checked Tommy’s Pronator Teres muscle. Even when Tommy was not pronating his forearm, his Pronator Teres muscle remained contracted.
Sweat contains higher concentrations of potassium electrolytes than body fluids. Therefore, sweating reduces the amount of potassium available to the nerve cells. The Potassium/sodium pump in nerve cells balances nerve conductions and relaxations. Therefore, when athletes have low potassium concentrations, their motor nerves continue to stimulate muscle contractions, that is, the muscles that these motor nerves serve cramp. I attributed Tommy’s Pronator Teres tauntness to potassium insufficiency. Unfortunately, Tommy was having an outstanding season and continued his training routine.
Two weeks later, when he threw a pitch to a Montreal Expo batter, Tommy’s pitching arm buckled. The pitch bounced halfway to home plate. After his next throw also bounced halfway to home plate, he walked straight to me and said, “You were right.”
I went with TJ the training room and examined his arm. Because the Pronator Teres, Flexor Carpi Radialis, Palmaris Longus, Flexor Carpi Ulnaris and the portion of his Flexor Digitorum Superficialis muscles formed a ball in the middle of the anterior surface of his pitching forearm, I determines that the attachments of these muscles had torn loose from the medial epicondyle of his Humerus bone.
When I applied sideways pressure to the inside of his pitching elbow, where the Ulnar Collateral Ligament attaches the medial epicondyle of his Humerus bone to the coronoid process of his Ulna bone, these two bones moved apart. Clearly, Tommy had ruptured his Ulnar Collateral Ligament. I told Tommy that he had seriously injured his pitching elbow.
Nevertheless, the next day, when I arrived at Dodger Stadium, I found TJ tossing a baseball to a catcher in the home bullpen. I immediately grabbed TJ and took him to the Bill Buhler, the Dodger trainer and I explained Tommy's problem. Fortunately, Frank Jobe, the team orthopedic surgeon, later confirmed my diagnosis and did corrective surgery.
e. Supinator
The tendon of the Supinator muscle attaches to the lateral side of the anterior surface of the proximal one-third of the Radius bone and to the lateral epicondyle of the Humerus bone, to the Annular Ligament of the head of the Radius bone and to the Supinator Crest and Fossa of the Ulna bone. Therefore, when the Supinator muscle contracts, these structure move closer together. This means that the Supinator muscle supinates the Forearm Joint.
Because, during the deceleration phase of the baseball pitching motion, baseball pitchers must safely return the pitching forearm to its normal resting position, the Supinator muscle supinates the Radius bone.
4. The Kinesiological Actions of the Forearm Joint During the Marshall Baseball Pitching Motion
During the acceleration phase of the Marshall baseball pitching motion, to prevent the olecranon process of their pitching elbow from slamming into its fossa, baseball pitchers need to powerfully mioanglosly pronate their pitching forearm.
During the deceleration phase of the Marshall baseball pitching motion, to safely decelerate and stop the powerful pronation of their pitching forearm through release, baseball pitchers need to powerfully plioanglosly supinate their pitching forearm. Remember, baseball pitchers can only pronate their pitching forearm as powerfully as the muscles that supinate their pitching forearm allow.
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