Throwing is like any other skill; it has generalizable phases – or sequences, if you will – that make up the finished product. The generalizable sequences of the overhead throw relate to all human beings regardless of activity and time period. It does not matter if one is throwing a baseball across the diamond, a football across the line of scrimmage, or a spear across the battlefield. Slight deviations in these sequences can lead to musculoskeletal quandaries, and these deviations can be the difference between a well-performed season and another name on the disabled list.

It is imperative for the overhead baseball or softball athlete – regardless of position – to understand the basic 6 phases that make up the defensive aspect of their sport. Below you will find a succinct breakdown of each phase of throwing.

Phase 1: The Windup

The windup starts in the double leg stance position and ends when the thrower is in a single leg stance position.  Appropriate hip muscle activation – involving an integration of strength, motor control, balance, and coordination – are essential to appropriate pelvic and lower extremity positioning during this phase of throwing.

Keys to this phase of throwing:

  • Center of gravity is over the stance (back) leg
  • Knee of stance leg is in slight flexion – this position is possible with adequate quadriceps strength
  • The stance-leg pelvis is level with or below the swing-leg pelvis – this position is possible with adequate hip abductor strength (a lateral hip muscle group that helps keep the pelvis level)

Deviations (pathomechanics) in the wind up that can lead to injury:

  • Insufficient hip abductor strength or motor control is associated with labral tears in upper corner (posterosuperior) throwing shoulder
  • Knee hyperextension of the stance leg can be associated with the dread UCL (ulnar collateral ligament) tear of the throwing elbow – often the impetus for Tommy John surgery.

Phase 2: Stride

Stride phase starts when the hands separate at the end of the wind-up and ends when the lead foot strikes the ground.

Keys to this phase for the legs:

  • Stride (front) foot is pointed towards the target
  • Stride leg, stance leg, and target should be in (mid)line with each other
  • Hip abductors of the stance leg initiate forward motion – followed by hip and knee extension
  • Gluteus maximus – the main buttocks muscle – assists in stabilizing the trunk and pelvis
  • The stance leg hip rotates internally while the stride-leg hip simultaneously rotates externally.

Keys to this phase for the arms:

  • Hands separate in this phase as we prepare to cock the arm for the next phase

Deviations (pathomechanics) in the stride phase that can lead to injury:

  • Insufficient stance leg internal rotation can lead to injuries in other joints
  • Excessive external rotation of the stride leg during foot placement is associated with anterior (front) shoulder instability, SLAP (labrum) tears of the shoulder, (that dreaded) UCL injury, and abdominal (obliques) strains.

Phase 3: Arm Cocking

Stride phase starts when the hands separate at the end of the wind-up and ends when the lead foot strikes the ground.

Keys to this phase for the legs:

  • Stride (front) foot is pointed towards the target
  • Stride leg, stance leg, and target should be in (mid)line with each other
  • Hip abductors of the stance leg initiate forward motion – followed by hip and knee extension
  • Gluteus maximus – the main buttocks muscle – assists in stabilizing the trunk and pelvis
  • The stance leg hip rotates internally while the stride-leg hip simultaneously rotates externally.

Keys to this phase for the arms:

  • Hands separate in this phase as we prepare to cock the arm for the next phase

Deviations (pathomechanics) in the stride phase that can lead to injury:

  • Insufficient stance leg internal rotation can lead to injuries in other joints
  • Excessive external rotation of the stride leg during foot placement is associated with anterior (front) shoulder instability, SLAP (labrum) tears of the shoulder, (that dreaded) UCL injury, and abdominal (obliques) strains.

Phase 4: Acceleration

This phase begins when the shoulder is maximally cocked in external rotation and ends when the ball leaves the hand. In this phase, the trunk moves from extension to flexion. The oblique and abdominal muscles on the non-throwing side are active.  The pectorals and latissimus (lats) help to internally rotate the arm, eventually leading to release of the ball. Maximum shoulder internal rotation of the shoulder occurs just before extension of the elbow, increasing the velocity of the throw.

Deviations (pathomechanics) in the acceleration phase that can lead to injury:

  • Hyperextension of the lumbar spine can lead to hyperextension-related pathology (spondylolisthesis/spondylolysis) and can also create a “slow arm”.
  • Elbow below the shoulder can lead to UCL injury and/or shoulder impingement

Phase 5: Deceleration

The deceleration phase begins when the ball leaves the hand and ends when shoulder is in maximum internal rotation. The rotator cuff musculature in the back of the shoulder (coined the “posterior rotator cuff muscles”) dissipate large forces to decelerate the throwing arm as it crosses the body. Most overuse injuries related to throwing occur during this phase.

Effect of the forces during this phase on the posterior rotator cuff:

  • These muscles externally rotate the arm and are responsible for controlling the internal rotation that is occurring at a high velocity as the ball leaves the hand. These muscles tend to thicken in response to the forces they must dissipate during this phase. This thickening is another fact that can lead to limited internal rotation range of motion in the throwing shoulder.

Injuries associated with this phase:

  • SLAP (labrum) injuries of the shoulder
  • Bicep, brachialis, and teres minor injuries (tendinopathy or tear)

Phase 6: Follow-through

This phase occurs when the body weight is transferred to the stride leg. The body is still decelerating and balancing over the stride leg. Abruptly stopping the throwing arm would cause larger amount of force to be absorbed by the shoulder.

Basic knowledge of these six phases should be grasped by any baseball or softball athlete, coach (strength and conditioning, pitching, and head), trainer, or rehabilitation specialist. Whether looking to mitigate injury heading into the new season, staying healthy while in season, looking to increase performance, or rehabbing from an injury, you should seek out a movement specialist that has an intimate understanding of throwing mechanics and can design treatment programs that focus on deficiencies specific to the corresponding phases of throwing.

    References:

    • Myers JB, Laudner KG, Pasquale MR, Bradley JP, Lephart SM. Scapular position and orientation in throwing athletes. Am J Sports Med. 2005;33(2):263-271.
    • Seroyer ST, Nho, SJ, et al. The Kinetic Chain in Overhand Pitching: Its Potential Role for Performance Enhancement and Injury Prevention. Sports Health. 2010 Mar; 2(2): 135-146.
    • Stodden DF, Fleisig GS, McLean SP, Lyman SL, Andrews JR. Relationship of pelvis and upper torso kinematics to pitched baseball velocity. J Appl Biomech. 2001;17(2):164-172.
    • Will K, Reinold M, Andrews J. The Athlete’s Shoulder.  2nd Edition. Churchill Livingstone; 2008.