What Muscles Are Used In Throwing A Baseball?

Along with a variety of other muscles throughout your body, those that control the bones of your shoulder girdle, shoulder joint, upper arm, forearm and hand play a key role in the baseball throwing motion. Understanding where these muscles are located and how they function can guide you in designing and implementing a training program to improve your throwing accuracy and velocity, and help prevent throwing-related injuries.

Latissimus Dorsi

The latissimus dorsi muscle spans the entire length of your back on either side of your spine, stretching from the top, front portion of the humerus bone of your upper arm to various structures within the lower back and on your pelvis. The latissimus dorsi acts to inwardly rotate your upper arm during the acceleration phase of the throwing motion, before you release the ball. Additionally, the muscle helps to slow down your throwing arm during the deceleration, or follow-through, phase, after you've released the ball.

Teres Major

The teres major muscle attaches to the front of your upper arm, near the attachment of the latissimus dorsi muscle, crosses under the shoulder joint and reattaches to the lower, inside portion of the back of the scapula bone within the same side of your upper back. The teres major muscle acts in cooperation with the latissimus dorsi muscle during the baseball throwing motion, working to inwardly rotate the humerus bone during the acceleration phase and decelerate your arm during the follow-through phase.

Triceps Brachii

The triceps brachii muscle, or just triceps, lies on the back of your upper arm and consists of three strands -- the medial head, lateral head and long head -- which attach to the bottom two-thirds of the humerus bone, the top half of the humerus bone and just behind the shoulder joint, respectively. All three heads combine at their lower ends and attach to the olecranon process -- the bony protrusion on the back of your elbow. The proper baseball throwing motion utilizes the triceps muscle to powerfully extend your forearm during the acceleration phase.

Wrist Flexors

The flexor carpi radialis and flexor carpi ulnaris muscles lie on the palm side of your forearm and contribute to wrist flexion, which occurs when you move your palm toward your elbow. The palmaris longus also contributes, but it's not always present in the throwing forearm. All three muscles attach to the medial epicoldyle of the humerus bone -- the bony protrusion on the inside of your elbow -- and run down the entire length of your forearm. The wrist flexors contract at the end of the acceleration phase of the throwing motion, just before and as you're releasing the ball.