The Muscles Used to Throw a Baseball
Bringing the ball back:
The Posterior Deltoid causes the Glenohumoral Joint (shoulder) to horizontally adduct
and externally rotate. The Anterior Deltoid stretches to slow the external rotation and the
Pectoralis Major stretches to slow the horizontal adduction. Also, the Back Extensors and
Obliques cause trunk rotation.
In the lower body, the Rectus Femorus and Illiop Psoas flex the hip, bringing the leg up.
Throwing the ball:
The Pectoralis Major and Anterior Deltoid work in conjuction to both internally rotate
and horizontally abduct, moving the ball forward. At the same time, the Triceps Brachii
extends the elbow, providing more forward vectors. Also, the Abdominals and Obliques
rotate the trunk toward the throw, also increasing forward vectors.
On the lower body, the Quadriceps extend the Femorotibular joint (knee) and the Glutes
extend the hip, which further increases the forward vectors.
Recovery:
The Posterior Deltoid must undergo massive stretching to slow the motion of the arm (the
reason for common Anterior Shoulder Subluxations*). The rear leg comes off the ground
involuntarily to balance the throw and to bring the pitcher back to a normal position.
*partial dislocation: a partial dislocation of bones that leaves them misaligned but still in some
contact with each other.