Some studies relating velocity to arm action:
A number of studies that correlate throwing velocity with external rotation of the shoulder. External rotations approaching 180° correlate to highest velocity. The normal clinical assessment range of motion, clinical assessment meaning the range of motion that can be achieved by simply trying to rotate the shoulder, is in the range of 115-120°.
So the question then becomes how does a player with a normal extra rotation of less than 135° achieve extra rotations in throwing that approach 180°?
The answer is simply that the inertia of the forearm wanting to lay back i.e. stay back, as the upper body rotates, that creates the added force necessary to twist the humorous backward to create the necessary or desired external rotation.
Another study found that maximum velocity correlates to the angle of the upper arm with respect to the shoulders. That angles less than 90° produce less velocity.
Also found in the study, was that there was no difference in stress between angles of 90° versus angles less than 90° (elbow below the shoulder level during the delivery).
Throwing the baseball is walking the injury tightrope……You can’t get something for nothing
There is a price to pay for this external rotation and that price is, valgus torque on the elbow.
- It is believed by many researchers/clinicians that valgus torque during the throwing process produces much of the stress on the ulna collateral ligament (UCL).
- And it’s also believe that this stress is a significant contributor to elbow injury requiring Tommy John surgery or UCL replacement.
It’s important understand that trying to measure and predict forces in joints and connective tissues of the body is extremely difficult.
The two primary methods that are accepted by most researchers are either:
- “in situ” measurements: refers to the actual invasive procedure to implant measurement transducers to directly measure forces in connective tissue.
- Inverse kinematics analysis: Inverse kinematics relies upon specialized video equipment and software to decompose movement patterns into their respective kinematic and kinetic factors (velocity, acceleration, force). Inverse kinematics is an indirect measurement process which is subject to the accuracy of the modeling software used to do the analysis.
Any other attempts to predict connective tissue forces or stress are speculative at best.
Based largely on inverse kinematics analysis it’s been determined that maximum stress on the elbow occurs just prior to maximum external rotation of the shoulder.
Figure 8: Where maximum stress on the elbow occurs in the pitching delivery.
A recent article appearing in Collegiate Baseball News compares what the author “termed” the inverted W of Strasburg and the “swinging” arm action of Mariano Rivera. His contention being Rivera did not lift his elbow above his shoulder and this was the mechanism that kept him injury free.
Figure 9: Mariano Rivera and Stephen Strasburg Maximum Stress Points in the Delivery.
If you compare Strasburg and rare at same point in the delivery, the point at which they achieve maximum external rotation, you will see…..
that there is virtually no difference in elbow position with respect to the shoulder.
From the research studies we know that at this point where both pitches of achieved maximum external rotation is the point in the delivery where maximum stress on the UCL occurs.
In other words starting with the elbows higher prior to achieving maximum external rotation does not lend itself to increase UCL stress as defined by research studies.
The real inverted W
The actual model for the inverted W came from John Smoltz. I observed John Smoltz would take the ball out of the glove by lifting the elbows up and back. As he progressed in his throwing sequence and began upper body rotation, the forearm would begin to elevate from an inverted downward position upwards. The elevation would continue as the upper body rotation continued.
Figure 10: John Smoltz delivery sequence.
From a physiological and physics perspective, starting the forearm from an inverted position allows a “jumpstart” to obtaining maximum external rotation. A jumpstart as opposed to an static arm action that was advocated as going to the high cock position where the player would hang his arm up keep it there prior to the initiation of upper body rotation, thus starting from a stagnant or zero forearm velocity position.
This goalpost arm action disconnects the arm from body actions taking place prior to going to the high cocked position.