By Courtney Semkewyc (RPP Bio-mechanist Intern, PhD Candidate Biomedical Engineering)
Hip and shoulder separation is a major contributor to efficient pitching / hitting mechanics, and a big piece of the puzzle to all things velocity. In this two-part article, we are going to review the relevance of several metrics on this subject using motion capture data charts as follows:
- Timing of the Max Hip-shoulder Separation Peak
- Max Value of Hip-shoulder Separation
- Kinematic Sequence as it Relates to Hip-Shoulder Separation
- Separation Time
What is hip-shoulder separation?
Hip-Shoulder separation is the difference between the shoulder angle and hip angle in the transverse plane (z-direction), which is characterized by when you turn your shoulders or hips to the left and right. Maximum hip-shoulder separation typically occurs around foot plant, and as such for a left-handed pitcher this value is the difference between how open their hips are towards home plate, and how closed their shoulders are facing first base as can be seen below.
Why is it important?
Hip-shoulder separation creates and stores energy to be used by the body later in the pitching motion. Muscles and fascia have an elastic component that allows them to act like a spring. As they are stretched, they build up energy that is released as they return to their original length. Think of your oblique abdominals as a spring, and as you counter-rotate your torso during leg lift you are beginning to stretch this spring and creating stored energy. Then as you begin to stride and load your scapula into horizontal abduction this will further counter-rotate your torso leading to additional stretch of the “spring”.
Finally, just before foot plant you begin to rotate your hips open towards home plate, while leaving your torso closed increasing the stretch even more. After foot plant, this increase in angle will result in maximum stretch of the “spring”, which will then be used to accelerate or slingshot the torso and arm towards the hips into an open position.
The energy that was stored by the spring is transferred into the torso during this acceleration phase, then up into the arm, and ultimately into the ball at release. It should be noted that more hip-shoulder separation isn’t always better as the amount of separation is dependent on an athlete’s anthropometrics and will be discussed later in this article.
Hip-shoulder Separation Causing Torso Whip
Can everyone create the same amount of hip-shoulder separation?
Hip-shoulder separation is dependent on an athlete’s anthropometrics, and as such not everyone is able to create the same amount of separation. Pitchers that have a longer torso tend to have longer muscle fascia enabling them to stretch more and have a larger hip-shoulder separation than pitchers with a shorter torso. As a result, pitchers should not try to achieve a hip-shoulder separation value that is outside their bodies natural range as this can lead to disruption of the stretch-shortening cycle and core instability.
A significant part of success on the mound is the importance of stability. Each segment throughout the pitching motion must be stable to support the motion of the successive segment. Trying to stretch the trunk beyond its limitations will result in muscle slack, where the muscle fascia are no longer coiled tightly, which in turn can result in a loss of stored energy. This will also cause an unstable trunk that will not efficiently transfer energy up the chain and have a hard time with proper acceleration/deceleration. Since hip-shoulder separation is athlete dependent, more hip-shoulder separation isn’t always better, and an athlete’s physical range needs to be established to determine good separation for them.
For a more in depth look into what it takes to create good hip-shoulder separation check out this prior article titled “Not All Hip and Shoulder Separation is Created Equal”.
Hip-Shoulder Separation Graph
A hip-shoulder separation graph depicts the difference between the hip angle and shoulder angle throughout the pitching motion. In this graph the blue vertical line is foot plant, and the red vertical line is release. There are two key things to look for in this graph:
- Timing of the Max Hip-shoulder Separation Peak
- Max Value of Hip-shoulder Separation
1. Timing of the Max Hip-shoulder Separation Peak
The timing or sequence of max hip-shoulder separation is important for efficient energy usage and provides insight into both the rotation of the hips and the torso. The hip and trunk rotations determine where the max hip-shoulder separation will occur in time. Pitchers typically begin to open their hips just before foot plant, and this trend is fairly consistent between pitchers. In other words, the pitcher may be early or late with their hips in terms of how open or closed they are approaching foot plant, but almost all pitchers begin to rotate their hips before foot plant. This allows them to open into foot plant putting their pelvis in the proper position in order to stabilize and both accept and transfer energy from the lead leg (and ultimately the ground) at foot plant.
Start of Pelvis Rotation Before Foot Plant
Since almost all pitchers begin hip rotation before foot plant, they are increasing the stretch of the spring and hip-shoulder separation. This means that the factor that would reduce hip-shoulder separation is trunk rotation. As a result, maximum hip-shoulder separation occurs when the torso velocity is equal to the pelvis velocity. This is due to the fact that once the trunk is rotating faster than the hips it will begin to close the gap reducing the angle between them and causing a decrease in hip-shoulder separation (more on this in Part 2).
The point in time when a pitcher “begins his trunk rotation” will impact when max hip-shoulder separation will occur. The longer the pitcher can keep their trunk closed and resist rotation the later the max hip-shoulder separation will occur. There are three distinct points in time at which max hip-shoulder separation can occur:
- Before Foot Plant
- At Foot Plant
- After Foot Plant
Before Foot Plant – Having max hip-shoulder separation happen before foot plant means that the pitcher is starting to rotate their trunk early. Early trunk rotation means that they are trying to transfer energy up the kinetic chain before foot plant. This is a problem as you want to begin this transfer of energy once you are anchored to the ground and have a stabile pelvis to rotate around. Efficient energy transfer and sequencing is a product of beginning a distal segment once the proximal segment is stable. Trying to rotate around an unstable base can lead to energy loss and timing problems, which can cause an increase in the likelihood of injury and a decrease in ball velocity. The early trunk rotation seen in hip-shoulder separation before foot plant can also be a sign of flying open, which can cause problems with both power and command.
If max hip-shoulder separation occurs before foot plant, then the amount of hip-shoulder separation that is actually contributing to the whip of the torso is the amount of hip-shoulder separation at foot plant once the lower body begins to stabilize. This means that the pitcher is leaking energy by not utilizing all of their max hip-shoulder separation.
The pitcher below reaches a max hip-shoulder separation of 52º, but since he is starting his trunk rotation early, by the time he reaches foot plant his hip-shoulder separation has reduced to 40º. This represents a 23-percentage point reduction of their max hip-shoulder separation prior to foot plant, which will result in less stretch to effectively rotate the torso around a stable pelvis.
At Foot Plant – Having max hip-shoulder separation at foot plant means that the trunk is only slightly early, and that energy can be more efficiently transferred as the front foot is anchored to the ground.
After Foot Plant – The optimal timing of max hip-shoulder separation is after foot plant and is the least common max hip-shoulder separation timing we see. This is mostly because it is very difficult for pitchers to resist trunk rotation until foot plant. It is also why the most common timing we see during our Mocap analysis with respect to max hip-shoulder separation is before foot plant.
Being able to start trunk rotation at or slightly after foot plant allows the upper body to rotate around a stable base, provides the pelvis more time to build up velocity and stored energy, and increases the separation time between peak pelvis and peak torso angular velocities.
2. Max Value of Hip-shoulder Separation
The second topic to look for in the hip-shoulder separation graph is the max value. Generally, 35-60 degrees of peak hip-shoulder separation appears to be optimal.
As stated earlier, these values are player-dependent though and depend on torso length. So, while 35º of hip-shoulder separation may be optimal for a pitcher with a shorter torso this would not be sufficient for a pitcher with a longer torso and fascia that could easily achieve 50º of separation. It is important to know your athlete and assess their anthropometrics when trying to determine their optimal level of hip-shoulder separation. It is not only important to look for a value of max hip-shoulder that sits within an individual’s range of trunk mobility, but also that works best with the timing of their mechanics.
Another important factor is that a pitcher should only have a large hip-shoulder separation if their torso is then able to close the gap through its angular velocity. There is no point in creating such large separation if the torso can’t get into the correct position for max external rotation and release. Both exceeding physical limitations and not being able to get into proper positioning can lead to timing problems and increase in the risk of injury to the arm. Increasing hip-shoulder separation is a good method to increase the potential energy stored in the stretch of the torso, but it must be done taking into consideration an individual’s physical limitations.
Max hip-shoulder timing after foot plant allows for an efficient kinematic sequence and distribution of energy throughout the body, which can lead to an increase in velocity and reduction in the risk of injury. The value of hip-shoulder separation provides potential energy to be converted into the angular velocity of the torso with an increase in separation leading to an increase in stretch and potential energy. If a pitcher is able to delay their trunk rotation until after foot plant this will put their pelvis into a stable position for transfer of the stored energy into the trunk. Being able to combine this delayed rotation with a good amount of hip-shoulder separation is the key to being able to create, store, and efficiently transfer energy up the kinetic chain.
Please stay tuned for Part 2, where we’ll get into the kinematic sequence, separation timing and sequencing.
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