What is Hip Shoulder Separation?

Throwing a baseball has been shown to be the fastest motion in all of sports. The velocities achieved during the pitching motion lead to excessive torques, or twisting forces, at the shoulder and elbow joints that can lead to injury. Previous blogs have addressed the relevance of shoulder flexion (click here) and hip flexion (click here) range of motion for mitigating injury risk. Another mobility consideration is that of the thoracic spine, which is necessary for achieving hip shoulder separation. Prior to defining hip shoulder separation, let’s quickly review the pitching delivery.


The pitching motion can be broken down into six different phases: the wind-up, stride, arm cocking, arm acceleration, arm deceleration, and follow through (9). The wind-up begins when the pitcher first initiates their motion and ends when they achieve maximal knee height. During this phase, the torso and the pelvis are in a closed position (8). For a right-handed pitcher, this would mean that they are facing towards third base; for a left-hander, they would be facing first base.



The next phase of the pitching delivery, the stride, is initiated as the lead leg begins to fall towards home plate and the pitcher begins to separate their arms. As the stride is initiated, the lead hip begins to externally rotate while the back hip begins to internally rotate. This results in the pelvis turning to face home plate. The torso, however, continues to remain in a closed position as the pitcher reaches front foot contact, indicating that upper torso rotation is delayed (8). The torso remaining closed as the pelvis turns toward home plate is what we refer to as hip shoulder separation, which, as we will discuss shortly, can play a crucial role in generating high velocities on the mound while limiting the amount of torque experienced at the shoulder and elbow.



The stride phase is followed by the cocking phase. As the cocking phase is initiated, the torso begins to rotate towards home plate as the throwing shoulder achieves maximal external rotation. The torso rotating towards home plate as the shoulder rotates towards second base is what allows a pitcher to store potential energy that is later released as they progress into the acceleration phase. Unfortunately, though, the torso and shoulder moving in opposite directions during the cocking phase is also what leads to the large torques experienced at the shoulder and elbow during the pitching motion (1,4). This is a critical moment in the pitching delivery.



Pitchers are able to generate momentum by sequentially utilizing the larger body segments (8). Achieving proper hip shoulder separation is one critical moment in the pitching delivery that can lead to improved efficiency by maximizing the contributions of the hips, pelvis, and trunk. By doing so, pitchers are able to increase throwing velocities and minimize the amount of stress placed on the shoulder and elbow in the process (1). Using the larger, more proximal muscles to generate force prior to transferring this force to the smaller, more distal segments is a concept commonly referred to as kinetic linking.


Kinetic Linking


Kinetic linking follows the summation of speed principle, which dates back to at least 1972 when John William Bunn wrote “Scientific Principles of Coaching” (6). The summation of speed principle states that in order to maximize the speed of the distal segment while throwing or striking an object, the movement should start with the more proximal segments. As the proximal segment reaches its maximal velocity, the next segment in the kinetic chain initiates its movement, leading to a maximal speed greater than that of the prior segment. This sequence repeats itself until the velocity at the distal end of the kinetic chain is built up by summing the individual speeds of each segment that contributed to the movement. “When segments move in sequence, the more proximal segments do not make large kinematic contributions to the distal end velocity at the instant of impact or release, but their motion histories are such that they make it possible for the distal end to achieve high velocities” (6)



The pitching delivery is a beautiful example of the summation of speed principle in action. It also illustrates the importance of hip shoulder separation. During the throwing motion, force is generated by the lower extremity of the drive leg before being transferred to the trunk and eventually the upper extremity of the throwing arm. So long as the timing is correct, the momentum generated early in the pitching delivery is able to be transferred efficiently to the more distal segments. The more segments that contribute to this process, the greater potential velocities a baseball pitcher is able to achieve (9). In this sequence, rotation of the trunk will ideally begin after maximal angular velocity of the pelvis has been achieved (7). If hip shoulder separation is not achieved, trunk rotation occurs prematurely, resulting in potential energy being lost. This can have negative effects on pitch velocity as well as shoulder and elbow torques.


Success Leaves Clues


Not surprisingly, professional baseball pitchers have been shown to do a better job of achieving hip shoulder separation than lower-level pitchers (1,4). The ability to achieve this position at the conclusion of the stride phase was shown in one study to increase fastball velocities by about 2.5 miles per hour (7). While that may not seem significant, that’s a pretty big deal, especially in today’s era of baseball that tends to reward pitchers who are able to light up a radar gun. One of the theories that does a good job of explaining why hip shoulder separation may increase fastball velocity pays close attention to the segmental velocities that are generated during the throwing motion. Pitchers who throw harder also demonstrate higher rotational velocities of the pelvis and trunk (8). Increased rotational velocities at the pelvis and trunk allows for more energy to be transferred to the more distal segments of the throwing arm, resulting in higher ball velocities.



Another benefit to achieving hip shoulder separation is the increased efficiency of the pitching delivery. This increased efficiency helps to limit the amount of internal rotation torque at the shoulder and the amount of varus torque experienced at the elbow (1,2,4,9). In fact, one study found that, when body mass was taken into account, high school pitchers actually experienced more elbow varus torques than professional pitchers at maximal external rotation (4). This is an interesting finding, as it shows that even though a professional pitcher is able to generate higher fastball velocities, they do so with less stress being placed on the throwing arm relative to their body mass. So not only does achieving hip shoulder separation help to increase fastball velocities, it also has the potential to mitigate injury risk.


Downstream Consequences of Not Achieving Hip Shoulder Separation


When trunk rotation occurs too early in the pitching delivery, hip shoulder separation is unable to be achieved. This is an error that many coaches refer to as “opening up too soon” (2). One potential reason for this error is front foot position at contact during the stride phase. Landing with the front foot in an excessively open position leads to pelvic rotation occurring prematurely (9). For a right-hander, this would mean landing with the front foot too close to first base; for a left-hander it would mean landing too close to third. The premature rotation of the pelvis can throw off the timing of the pitching delivery, resulting in the trunk rotating too early as well, which, as we mentioned, can lead to a loss of potential energy in the kinetic chain.



As potential energy is lost due to poor timing of the pelvis and trunk, the upper extremity makes a valiant effort to compensate for the deficiency (1). This is seen as a late whipping action at the shoulder joint during the acceleration phase, leading to more extreme ranges of motion at maximal external rotation as well as increased joint angular velocities (1,3,5). These increases in range of motion and angular velocity occurring at the shoulder have been shown to result in an increase in peak shoulder proximal force, which puts additional stress on the soft tissues structures surrounding the shoulder (2,5). These structures include the rotator cuff, joint capsule, and labral complex, which can sideline a pitcher for a potentially significant amount of time when injured.


Kinematic Considerations for Achieving Hip Shoulder Separation


A lot goes into achieving hip shoulder separation, with pitching mechanics being a big factor. In order to achieve these positions in the delivery though, the athlete needs to possess the requisite amount of motion at several different joints, including the hips and thoracic spine. We have already discussed hip mobility as it pertains to achieving a closed shoulder position (click here), so today we will focus our attention on thoracic mobility. The lumbar locked thoracic rotation test, which has been popularized by Function Movement Systems and the Titleist Performance Institute, has become one of my favorite ways to assess thoracic rotation range of motion. Start by having the athlete in a quadruped position. Instruct them to sit their butt to their heels and drop their forearms down to the table. Next, have them place one hand behind their back and rotate that shoulder towards the ceiling. Be sure to perform this test both actively and passively.



We can measure the degree of thoracic rotation by drawing an imaginary line through both shoulders so that it intersects the table. The degree between the table and the imaginary line will give us our degrees of thoracic rotation. For the general population, we are looking for about 50 degrees of thoracic rotation but for rotational athletes, such as baseball pitchers, we would like to see 70 degrees or higher. If an individual is limited actively but has full range of motion passively, like Hannah in the above video, we can label this a neuromuscular control dysfunction. This means that she possesses adequate range of motion but she is unable to tap into it fully. Individuals who present like this require exercise intervention that teaches them how to actively control their full range of motion. If the individual is limited both actively and passively, we would label it a tissue compliance or joint dynamics dysfunction (for more on developing a movement diagnosis, click here). These individuals benefit more from exercises that emphasize mobilization.



Foam rolling is a great option for mobilizing the thoracic spine. Start by having the athlete lie on their back with the foam roller resting in the middle of the shoulder blades. Next, instruct the athlete to give themselves a big hug, in order to take slack out of the system, then lift their hips off the ground and roll up and down (stay off of the lower back while performing this exercise). After rolling, have the athlete drop their hips back to the ground and place their hands behind their neck. The purpose of this hand placement is to support the weight of the head, do not crank on the neck. While keeping the lower back in a neutral spine position, have the athlete look up towards the ceiling in order to mobilize the thoracic spine into extension.



The Kettle Bell Rotation and Press is another great option for mobilizing the thoracic spine.

Start by having the athlete lie on their side with their knees bent to hip height. Have the athlete use the bottom arm to stabilize the top leg and use the top arm to hold a kettle bell in an arm bar position. Instruct the athlete to rotate the kettle bell towards their top shoulder and rotate their top shoulder towards the ground. Be sure to have the athlete keep the elbow in tight, as if they were squeezing a newspaper against their side, while performing this motion. Exhale at the bottom before returning to the starting position.



Once mobility is improved, we must then teach the athlete how to control the newly acquired range of motion. Kettle Bell Rotation Holds are a great option for teaching thoracic rotation neuromuscular control. Start by having the athlete hold a kettle bell in a rack position with the ipsilateral knee flexed to hip height. Use the opposite hand to rotate the trunk towards the flexed hip until resistance is felt. Once resistance is felt, instruct the athlete to let go of the knee and hold this position for three breathes. Repeat this process for two more repetitions before returning to the starting position.


Summary


The baseball pitching motion has been shown to be the fastest motion in all of sports. Baseball pitchers are able to generate these elite level velocities by coordinating multiple segments in the kinetic chain so that energy is transferred from the bigger, more proximal joints and muscles to the smaller, more distal ones. One of the key components in this energy transfer is achieving hip shoulder separation. Achieving this position has been shown to improve efficiency in the throwing motion, which can increase fastball velocity and reduce the amount of stress placed on the throwing shoulder and elbow. While pitching mechanics play a big role in achieving this position, we must first investigate whether our athletes possess the necessary range of motion to achieve this position in the first place. Hip and thoracic mobility should be assessed in all of our baseball pitchers to identify potential weak links in the kinetic chain. Only once these weak links are identified can we begin to build a rehab and training program to optimize performance and mitigate the risk of injury on the field.


Resources


1. Aguinaldo AL, Buttermore J, Chambers H. Effects of upper trunk rotation on shoulder joint torque among baseball pitchers of various levels. J Appl Biomech. 2007 Feb;23(1):42-51.

2. Davis JT, Limpisvasti O, Fluhme D, Mohr KJ, Yocum LA, Elattrache NS, Jobe FW. The effect of pitching biomechanics on the upper extremity in youth and adolescent baseball pitchers. Am J Sports Med. 2009 Aug;37(8):1484-91.

3. Douoguih WA, Dolce DL, Lincoln AE. Early Cocking Phase Mechanics and Upper Extremity Surgery Risk in Starting Professional Baseball Pitchers. Orthop J Sports Med. 2015 Apr 22;3(4):2325967115581594.

4. Luera MJ, Dowling B, Magrini MA, Muddle TWD, Colquhoun RJ, Jenkins NDM. Role of Rotational Kinematics in Minimizing Elbow Varus Torques for Professional Versus High School Pitchers. Orthop J Sports Med. 2018 Mar 20;6(3):2325967118760780.

5. Oyama S, Yu B, Blackburn JT, Padua DA, Li L, Myers JB. Improper trunk rotation sequence is associated with increased maximal shoulder external rotation angle and shoulder joint force in high school baseball pitchers. Am J Sports Med. 2014 Sep;42(9):2089-94.

6. Putnam CA. Sequential motions of body segments in striking and throwing skills: descriptions and explanations. J Biomech. 1993;26 Suppl 1:125-35.

7. Sgroi T, Chalmers PN, Riff AJ, Lesniak M, Sayegh ET, Wimmer MA, Verma NN, Cole BJ, Romeo AA. Predictors of throwing velocity in youth and adolescent pitchers. J Shoulder Elbow Surg. 2015 Sep;24(9):1339-45

8. Stodden DF, Fleisig GS, McLean SP, Lyman SL, & Andrews JR. Relationship of pelvis and upper torso kinematics to pitched baseball velocity. Journal of Applied Biomechanics. 2001;17:164-172.

9. Wilk KE, Meister K, Fleisig G, & Andrews JR. Biomechanics of the overhead throwing motion. Sports Medicine and Arthroscopy Review. 2000;8(2):124-134.