RESEARCH REVIEW: ELBOW BIOMECHANICS
The throwing motion is the single fastest motion in all of sport. It is also one of the most dangerous, and is not healthy for your arm. We love it so much, we continue to do it anyway!
If you read Power Pitching, you know that the throwing motion is broken up into 6 different phases. Since we also know that mechanics are not the end all be all to enhancing throwing velocity, what can we still learn about them?
Our elbow goes under a lot of stress and torque when we throw and release and a baseball. What happens during each phase?
Let’s review what the research says about elbow torque during each phase, and how we can strengthen our elbow to handle high forces.
The Windup and Stride
As the hands separate from each other when striding down the mound, the elbow flexors lengthen and then shorten towards the end of the stride. The end of the stride phase is when the front foot meets the ground.
When front foot contact is initiated, the elbow should be flexed between 80 and 100 degrees.
It’s also important to consider the amount of separation that a pitcher gets once the front foot is rooted into the ground. The front hip needs to separate from the back-throwing shoulder to stretch the anterior sling of the core.
This phase is between front foot contact and maximal shoulder external rotation. As the pitcher pulls from the glove side, the trunk is rotating towards the target and there should be little variance in elbow flexion.
If a pitcher constantly changes elbow flexion during this phase, there is even more torque added onto the elbow. The greater the external rotation of the shoulder, the more torque is put on the elbow.
Having a stronger lower half to accelerate and decelerate will take stress off the throwing arm. Once the arm cocking phase begins, the pelvis and torso rotate independently to face home plate.
The supinator and extensor muscles are the most active during this phase of the motion, so it is important to strengthen them eccentrically.
The elbow receives the most amount of compressive forces at ball release. Weak muscles on the medial (inside) aspect of the elbow can lead to a further increase in compressive forces at ball release.
Having a strong elbow is just as important as a strong shoulder!
This phase is when the shoulder moves from maximal external rotation to ball release. Although ball speeds may be different with different pitches, elbow angular velocity is basically the same.
Between fastballs, sliders, and curveballs, elbow angular velocities are quite similar. However, they are significantly less during the changeup.
When the arm rapidly extends at ball release during acceleration, its unlikely that these velocities are coming just from the elbow.
Since the body is undergoing a complicated series of movements, initiated from pelvic and torso rotation, these velocities are the energies that are left over from hip and shoulder separation.
Research has shown that the elbow contributes less than 43% to ball velocity during throwing! The largest contribution comes from body rotation.
This phase begins at ball release and ends at maximal shoulder internal rotation. The greatest forces during deceleration are the eccentric (lengthening) contractions of the elbow flexors to try and slow the arm down.
The biceps (that’s right, bro!) and other supinator muscles have a huge roll during arm deceleration: they are responsible for controlling the amount of pronation that occurs during maximal internal rotation.
This part of the throwing motion is just as important as the rest because this is when the rest of the body should absorb all the energy that it just produced to the ball.
The forces and joint torques that were seen during arm acceleration and deceleration are much less during the follow-through because the rest of the body is taking the force off (if we follow-through correctly, of course).
Now that we know what happens during each phase, hopefully we can appreciate that the elbow does take a good beating when throwing.
Proper coordination from the rest of the body will save your elbow. Not only will proper mechanics help you out, but having a strong elbow that is able to reduce and absorb all of the forces that are put on it.
How can we strengthen our elbow?
Here are a few exercises to help:
Supination and pronation
Farmers carry/Plate pinches
Jarad Vollkommer, CSCS
Fleisig, G.S. and Escamilla, R.F. (1996). Biomechanics of the elbow in the throwing athlete. Operative Techniques in Sports Medicine 4(2), 62-68.