Biomechanical Answer/Answer

Phase 1 (Wind-up):

-                Description:

The wind‐up phase begins when the pitchers makes their first movement from the static position of facing the batter with both feet on the rubber (Calabrese, 2013). The pitcher initiates the throw by stepping backward with the stride foot (left foot for right-handed pitcher) (Omar, 2016). The pitcher then turns his pivot foot to be parallel to the pitching rubber. Then, the stride leg is elevated, flexed, and drawn into the chest, with the lead side (left side for a right-handed thrower) facing the target (Braatz & Gogia, 1987). The windup phase ends when the lead knee has reached its maximum height (Diffendaffer et al., 2023).

 

Figure 4: Pivot foot and stride foot in the final position of wind up.

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Centre of gravity:

In the final position of the wind-up, the weight is shifted to the pivot leg. This allows the pivot leg to serve as a base of support. The hands and the head are positioned over the pivot foot. This position helps maintain the pitcher's balance by keeping the Centre of gravity over the pivot leg, ensuring stability and preventing the weight from prematurely shifting to the stride foot. This allows the generation of maximum momentum and power once forward motion is initiated (Seroyer et al., 2010). Leaning too far anteriorly or posteriorly can disrupt the kinetic chain, the body segment sequence timing, and affect proper energy transfer from the lower body to the throwing arm (Calabrese, 2013; Mayes et al., 2022).

Figure 5: Comparison of weight shift and center of gravity between a professional (right) and an amateur (left). They maintain the center of gravity over the pivot leg without excessively leaning forward or backward. Their body positioning shows that the pivot leg bears most of the pitcher's weight with the hand and head positioned directly over the pivot foot.

-       Maximum knee height:

When throwing from the wind-up, the pitcher builds up potential energy by lifting the lead leg to its maximum height (Dun et al., 2008). The higher the leg is lifted, the more gravitational potential energy is stored (Hamm, 2020). This is because the formula for gravitational potential energy is PE=mgh. When the pitcher lifts their lead leg higher, the height h increases, directly increasing the gravitational potential energy stored in the leg. This potential energy is later converted into kinetic energy as the leg accelerates downward (Dun et al., 2008). This kinetic energy is efficiently passed from the lead leg and the trunk to the throwing arm through proper coordination between the arms and lower body, resulting in increased pitching velocity and reduced stress on the shoulder and elbow (Dun, 2008). However, if the knee is raised too high, it can cause a loss of balance, or inability to stabilise the body. Instability or loss of balance in wind-up might impede muscle activation, optimal force development, and energy transfer, negatively impacting an athlete's throwing speed (Garrison et al., 2013). Therefore, the knee should be lifted to an optimal height (neither too low nor too high) to generate sufficient potential energy while maintaining balance. It is recommended that the maximum knee height should be approximately 60-70% of a pitcher’s height (preferably with lead hip flexion ≥ 90°) (DeFroda, 2016; Kazziha, 2021).

Figure 6: Comparison of maximal knee height and hip flexion between a professional (right) and an amateur (left). The professional exhibits greater hip flexion compared to the amateur, leading to a higher knee lift in the professional than in the amateur.

Phase 2 (Early cocking):

-       Description:

This phase initiates after the pitcher reaches maximum knee height (Diffendaffer et al., 2023). The pitcher pushes off the rubber while moving toward home plate. The lead knee initiates downward movement. Simultaneously, the athlete begins to swing their hands down and separate apart. The stride phase ends when the lead foot contacts the pitching mound.

 -       Stride length:

Stride length is a significant biomechanical parameter for establishing the timing of the kinetic chains and generating greater translational energy from the lower body to the throwing hand (Yanagisawa & Taniguchi, 2020). Stride length was calculated as a percentage of the participant’s body height, measuring from the back foot to the first place on the mound that the lead foot heel touches at initial foot contact. Baseball pitching research indicates that a longer stride length contributes to a higher ball velocity (Smith et al., 2017, Yanagisawa & Taniguchi, 2020). In particular, they found that pitch velocity increased 0.9 m/s for every 10% increase in stride length relative to body height (Manzi et al., 2021). Increasing the stride length results in more forward displacement (Van Trigt et al., 2018). This allows the pitcher to generate more linear momentum in an intended throwing direction (toward a home plate), which results in a higher ball speed (Van Trigt et al., 2018). Some research has suggested that the ideal stride lengths should range between 80% and 85% body height (Crotin & Ramsey, 2016).

Figure 7: Comparison of stride length with a professional (right) to an amateur (left). The professional exhibits a greater stride length relative to body height compared to the amateur.

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        Knee flexion:

When the stride foot contacts the ground, the knee of the stride foot should be slightly bent to absorb the landing force and reduce the potential for injuries to the knee joint (Tamura et al., 2021). However, previous research showed that increased knee flexion at initial stride foot contact can decrease ball velocity (Van Trigt et al., 2018). With smaller knee flexion angles, the knee and hip absorb less energy, allowing more of the ground reaction force to be harnessed for generating more speed/power, ultimately producing greater ball velocity (Dowling et al., 2022; Pollard et al., 2010). It is recommended that the lead knee should be flexed about 45° at foot contact (Diffendaffer et al., 2023).

 

Figure 8: Comparison of knee flexion angle with a professional (right) to an amateur (left). While the professional's knee flexion angle aligns with the recommended angle (45°), the amateur's angle is significantly smaller. This could potentially lead to injury and adversely affect their performance in the sport.

 

-           Stride foot angle:

The stride foot should land pointing towards home plate in a slightly internally rotated or “closed” position (facing third base for right-handed pitchers) (Diffendaffer et al., 2023; Christoffer et al., 2019, Seroyer et al., 2010). The excessively closed front foot can limit pelvic rotation, causing the pitcher to throw across their body (Seroyer et al., 2010). Open stride foot position can cause premature pelvic rotation and disrupt the kinetic chains (Diffendaffer et al., 2023; Christoffer et al., 2019, Seroyer et al., 2010). This affects the transfer of energy up the body, potentially decreasing pitch velocity. At foot contact, the foot should be internally rotated within a range of 19° ± 11° (Fleisig et al., 2006).

Figure 9: Comparison of stride foot angle between a professional (right) and an amateur (left). The stride foot of the professional is depicted in a slightly closed position, whereas the amateur's stride foot is in an open position.

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      Shoulder horizontal abduction:

Increasing shoulder horizontal abduction is associated with faster ball velocity (Manzi et al., 2023). This can be explained by using the basic principle of the stretch-shortening cycle (Anzmann, 2020). Horizontal abduction places a pre-stretch on the muscle that is involved in accelerating and throwing such as pectoralis, and deltoid (Anzmann, 2020). When these muscles are pre-stretched, they store elastic energy, which is then released during the subsequent contraction phase (Moritz & Farley, 2005). This allows muscles to generate greater force and power. However, horizontal abduction should be applied within a reasonable range because excessive horizontal abduction can put additional strain on the muscles, potentially causing tears and lesions. In professional pitchers, shoulder horizontal abduction ranges between 17° and 30° (Manzi et al., 2023).

Figure 10: Horizontal abduction.

Figure 11: Comparison of shoulder horizontal abduction between a professional (right) and an amateur (left). The professional's arm moves or stretches farther backward behind their body compared to the amateur's arm.

Phase 3: Late cocking

Description

In this phase will begin from the lead foot when it touches the ground and it finish when the maximum external rotation of the shoulder from the throwing arm, and that the maximum rotation will reach 170° (Diffendaffer et al., 2022).

If there is too much shoulder rotation at the foot, contact of the ground this will decrease the velocity of the ball speed that is pitched (Fleisig et al., 2017).

when the pitcher throws the baseball towards the batter, if the cuff tendons get pinched between the humeral head and the glenoid where it may cause a tear in the cuff tendon.  There is also a risk of injury within the elbow as there is various pitching techniques (Diffendaffer et al., 2022).

 

While in this phase that the humeral head is centred in the glenoid fossa as this will impact the imbalance the should of 90° where it could lead to an impingement or labral injury in the shoulder that the pitcher uses to throw the baseball (Fleisig et al., 2017).

In this phase it is important that the pelvis an the trunk would reach the maximum rotation velocities as this would help with the speed of the baseball pitch and the aim of the ball towards the batter. When there is minimum flexibility of the pelvis and the torso this would limit the rotation for the velocity of the pitch (Diffendaffer et al., 2022).

Phase 4: Acceleration

Description

The arm acceleration phase begins at the maximum shoulder rotation, and it ends at the ball release. When the arm is being accelerated forward to perform the pitch it uses muscles from the glenohumeral and the scapular (Escamilla et al., 2009)

To increase the ball velocity, it is important to be at the maximum shoulder rotation at a decreased time and at an increase trunk tilt when the ball is released. Through this phase the subscapularis reaches the maximum activity along with the accelerators that are in the arm and while the pectoralis major is an important part that will help with the velocity in throwing the baseball, where this will help with the internal rotation of the humerus that reaches forces that could be as high as 185% for the maximum muscle (Seroyer et al., 2010).

During this phase when the elbow flexes from 90° to 120° it will the extend to about 25° before the ball has been released. When the torso is being rotated and the triceps are being contracted the elbow will extend then the shoulder will start internally rotating to make the pitch (Seroyer et al., 2010).

Phase 5 and Phase 6: Deceleration and Follow through

The final stage is the Deceleration stage/ Follow through phase and commences when the ball is released and concludes with the dominant shoulder sustaining maximal internal rotation and 35% horizontal abduction (Meister, 2000). The elbow and shoulder muscular activity is less excessive in this stage compared to previous stages as upon releasing the ball the pitcher positions his body in a fielding ready stance. The stance side foot is all the way up off the ground in the follow through, whilst there is rotation of the trunk over the leading leg which is extended as the trunk of the body descends central towards home plate.

 

(Calabrese,2013)

 

Reaching a final position to be ready to field any potential balls that are hit back and be reactive to any balls is always the goal, and pitchers can achieve this with flexibility and lead side hip internal rotation range. If there are any mechanical issues in the earlier phases of the pitching stride direction stage it will commonly result in a flow through that is off-balance (Calabrese, 2013). The posterior deltoid, trees minor and infraspinatus eccentrically act as a restraint for the humeral head translation while the scapular stability during deceleration is aided by serrated and rhomboids when the arm is extended towards home plate in the follow through motion (DiGiovine et al, 1993). Although the deceleration phase is the shortest phases in the pitching motion it is perhaps the most dynamic. Shoulder rotation is applied internally reaching angles of close to 0 degrees. Eccentric rotator cuff contractions and horizontal arm abduction across the torso regulate the internal rotation that is seen during the deceleration phase. An electromyographic analysis of this pitching phase reveals that teres minor plays a major role in the deceleration of the humerus internal rotation. Due to an underdeveloped teres minor, young pitchers may find it difficult to decelerate their arms. As a result, they may compensate by increasing the horizontal adduction of their arms across their torsos in an effort to slow down their throwing arms. Overuse tendinopathy may develop as a result of this increase in horizontal adduction during deceleration. Shoulder forces shift from an anterior-superior to a posterior-inferior direction during arm deceleration in an effort to limit horizontal adduction and avoid humeral abduction (Keeley, 2008).

The eccentric action of the posterior musculature and capsular soft issue, which is required to help dissipate the extreme rotational forces, has been suggested by multiple authors as possibly causing GIRD, glenohumeral internal rotation deficiency. Reportedly, during follow through, the bicep reaches its maximum eccentric muscle activity to impede the pronating elbow and forearm from extending too quickly (Jobe et al, 1984). An eccentric (lengthening) contraction occurs when the force exerted on a muscle exceeds the force that muscles can momentarily produce. As the muscle contracts it forces the muscle tendon system to extend or lengthen (Lindstedt,2001).

The Deceleration of the arm phase comes upon release of the ball. A significant posterior shear force (40–50% of body weight) resists shoulder anterior subluxation during arm deceleration, while a large proximal force (30–40% of body weight) resists shoulder distraction. As the arm moves forward into the follow-through phase, the eccentric forces aid in its quick slowing down. Exercises such as side lying external rotation with resistance, prone rowing into external rotation, ball catching over the shoulder with a plyometric ball, plyometric ball throws into the wall with a resistance band to provide eccentric muscle firing, and plyometric ball throws are specific ways to train the shoulder external rotators to control the arm eccentrically during deceleration. The body continues to move forward during follow-through until the arm stops moving. The elbow will "rebound" to roughly 45° flexion during this phase. When a ball is thrown back at them, the pitcher should finish the follow through in a position where they are prone to field the ball (Wilk et al, 2023).

To avoid harm, the kinetic energy produced during the acceleration phase needs to be released safely. For these forces to be distributed efficiently, the lower body, trunk, and upper body must work in unison through the kinetic chain. By distributing energy throughout the body's segments, proper technique lessens the strain on any one joint or muscle group.

Pitching deceleration is essential for avoiding injuries and maximizing output.

The deceleration phase, which happens right after the ball is released, is crucial for releasing the strong forces produced during the throwing motion. Eccentric muscle activity is used in this phase to minimize stress on the musculoskeletal system, prevent hyperextension, and slow down the arm and stabilize the shoulder joint. The posterior shoulder muscles and the rotator cuff are important muscles in the deceleration process, that needs to work in unison to impede the forward momentum. Joint stability and coordinated muscle activation are necessary for proper deceleration mechanics. Inadequate muscle conditioning or poor technique can raise the risk of shoulder injuries like labral damage or rotator cuff tears (Dillman etal,1993).