Pitching Mechanics
In total, there are six phases to an overhead pitching movement for baseball players. These phases include wind-up, early cocking (or stride), late cocking, acceleration, deceleration, and follow through. Poor biomechanics through any one of these phases has the potential to lead to injury, so proper instruction is important to help the athletes stay healthy.
Wind-Up Phase
The wind-up phase begins when the pitcher makes their first movement from facing the batter to being lateral with the batter, and ends when the pitcher’s lead leg reaches maximum knee height. Although there is barely any shoulder motion involved, this phase requires the batter to find their balance point, which is important in the pacing of the rest of the motion. If the pitcher moves out of the balance point too late or too early or simply begins to fall out of balance, the entirety of the pitching motion will be disrupted, leading to a poor pitch or even injury.
Early Cocking (Stride) Phase
The early cocking phase begins with maximum knee height, and ends when the pitchers lead leg makes contact with the ground. The stride phase is responsible to up to 50% of the balls velocity, so proper lower extremity, trunk, and shoulder positioning is extremely important. A short stride results in decreased potential trunk rotation, limiting the potential velocity of the pitch. Flexibility is important to allow for increased stride length, and is most important in the hamstrings, hip extensor, and hip external rotation muscles. The pitchers lead foot should land in a position that is almost directly facing home plate, and is rotated towards third base. If not in proper position, shoulder and trunk rotation may not occur to the full extent, increasing shear forces on the shoulder during the movement. The angle between the elbow and the trunk should be between 80-100 degrees, and during this phase scapular and humeral head stabilizers are firing to hold the joints in position.
Late Cocking Phase
The late cocking phase begins with lead leg contact with the ground, and ends with maximum external rotation of the shoulder. The trunk begins to rotate back towards the plate, beginning the forward motion. The shoulder externally rotates from 50 to up to 185 degrees during this phase. humeral head stabilizers fire to maintain position of the humerus in contact with the glenoid fossa. The subscapularis, latissimus dorsi, and pectoralis major all eccentrically contract to control the amount of external rotation. Throughout the motion, body weight is shifted onto the forefoot as the rear foot begins to push off and propel the body.
Acceleration Phase
The acceleration phase begins with maximum external rotation of the shoulder, and ends with release of the ball during the pitch. The acceleration phase of pitching is one of the fastest overall movements of the human body. The trunk continues to rotate during this phase towards the batter. Internal rotation occurs at speeds up to 9000 degrees per second, and this motion is completed through concentric muscle contractions of the latissimus dorsi and pectoralis major. The serratus anterior is important in maintain scapular position throughout the movement. If the hand and elbow sage behind the body during this motion, there is increased valgus force placed upon the elbow joint, potentially resulting in UCL injury.
Deceleration and Follow-Through Phases
The deceleration and follow-through phases begin with the release of the ball, and end with maximum internal rotation and approximately 35 degrees of shoulder adduction. This phase requires extreme amounts of eccentric contractions for shoulder external rotation, to slow down the arm. This remains true for scapular positioning as well, as the serratus and rhomboid muscles control the scapular positioning through eccentric muscle contraction. During this phase, the rotator cuff muscles must fire to prevent distraction of the humeral head out of the glenoid fossa, but fatigue may limit their contraction strength, potentially leading to injury.