The Kinematic Sequence - Proximal to Distal (Part 2)

In my previous post, we introduced the body parts associated with the Kinematic Sequence. In this blog, we will dive into research regarding the timing of the body segments in hopes to uncover their importance in generating power (velocity). Consider this a deeper dive into the value of Proximal-to-Distal within the Kinematic Sequence.

In February 2019 Dr. Arnel Aguinaldo and Dr. Rafael Escamilla published research out of Point Loma Nazarene University in San Diego on this very topic.

This research dives into the importance of sequencing as it regards to the generation of power/velocity. The paper segmented the delivery into six pieces and compared these pieces among high school pitchers and professional pitchers. The following is an excerpt from the article explaining their modalities.

“To assess the proximal-to-distal sequence in segmental body motion during the pitch, we collected the time points at which the maximum values of pelvis rotation velocity, trunk rotation, trunk rotation velocity, elbow valgus torque (MEV), shoulder external rotation (MER), and shoulder internal rotation velocity (MIRV) of the throwing shoulder occurred during the pitching cycle (PC), normalized from front foot contact to ball release.”

In this excerpt, we find our magical term -- Proximal-to-Distal. Before we go any further, let's review exactly what that phrase means. The term proximal is defined as body parts situated nearer to the center of the body (i.e. torso and hips), and distal as body parts situated further away from that center point (i.e. legs and arms). During an efficient delivery, the proximal pieces fire first and are responsible for delivering the distal pieces of the anatomy to finish the Kinematic Sequence. Now, let’s take a closer look at the six physical components of the delivery used to compare pro pitchers and high school pitchers.

Pelvis Rotational Velocity - the point in the delivery when the pelvis is rotating at its highest speed

Trunk Rotation - the point in the delivery when the torso begins to rotate

Trunk Rotation Velocity - the point in the delivery when the torso is rotating at its highest speed

(MIRV) Shoulder Internal Rotation Velocity - the point in the delivery when the throwing arm shoulder is internally rotating at its highest speed. Internal Rotation of the throwing arm shoulder is higher as it approaches 0-degrees.

(MER) Maximum Shoulder External Rotation - the furthest the throwing arm shoulder can “layback”, the point where the throwing arm is as close to parallel with the ground as possible. External Rotation of the throwing arm shoulder is higher as it approaches 180-degrees. The amount of stress imposed on the shoulder and elbow appears to be directly correlated with the degree of maximum shoulder external rotation (MER) during throwing motions.

(MEV) Elbow Valgus Torque - the point in the delivery where maximum force is applied to the medial side of the elbow. Elbow Valgus Torque is important because it has a direct relation to the strain applied on the Ulnar Collateral Ligament, the ligament involved in Tommy John surgery. The bending moment about the elbow joint would cause an increase in compressive force on the lateral structures and an increase in tensile force on the medial side.

Let's take a look at some of the results of the study. The two-timing points in the delivery used as references were Front Foot Contact (FC) and Ball Release (BR). FC is the moment the lead leg foot hits the ground & BR is the moment the athlete releases the baseball. The further to the left a triangle or square is, the earlier in the delivery it occurred. The further to the right a triangle or square is, the later in the delivery it occurred.

We are looking for the parts of the delivery that have the biggest difference between professional pitchers and high school pitchers. In order to do this, we will look to see within each body movement which of the squares and triangles are the furthest distance apart from each other.

The two segments of the body that have the biggest difference between professional pitchers and high school pitchers are Maximum Pelvic Rotation and Trunk Rotation. For High School pitchers, maximum trunk rotation appeared significantly earlier than in professional pitchers. Maximum Pelvis rotation velocity also appeared significantly earlier in high school pitchers than in professional pitchers.

The two most proximal segments of the body, the torso, and pelvis were the largest delineating factors in identifying the difference between an amateur's delivery and professional delivery. The timing of distal segments, such as the shoulder and elbow, was similar in both amateurs and professionals.

So what do these concepts look like in a delivery?

“Delayed” Trunk Rotation - Keep Front Side Closed into Front Foot Contact

Above is an image of some of the greats at front foot contact. All of their torsos are “closed” AKA the reliable old school cue of “keeping the front side closed”. Pitchers whose torsos rotate before front foot contact can be identified by having their chest pointing the catcher as the front foot hits the mound. This is something a coach will want to address with their pitcher immediately, as this position can put an inordinate amount of stress on the UCL & Labrum, and a strong indicator the athlete is at an increased risk of injury.

“Delayed” Max Pelvis Rotation Velocity - Pelvic Rack maintains Stacked for Longer Down the Mound

High School Pitcher Professional Pitcher

Pitchers who can keep their pelvic rack stacked down the mound longer will experience Max Pelvis Rotation Velocity later in their delivery. One of the large indicators that the pelvis has yet to rotate is “Back Foot Connection”. Making sure the back heel stays connected to the ground through the stride phase is an indication the pelvis rack has yet to rotate.

It is important to note, one can keep the Pelvic Rack closed for too long. If the pelvic rack opens up late, it can cause an inefficient lead leg block. The pelvic rack must be open to home plate just before front foot contact in order for the lead leg to efficiently block. If the pelvic rack is closed, the lead leg will have difficulty extending through ball release, thus leaving mph on the table. A coach wants to make sure an athlete maintains a back heel connection through the stride phase, but no longer.

But, when it comes to the differences one primarily sees between an amateur delivery and a professional delivery, the amateur's pelvic rack more often than not rotates sooner than the professional's.

I believe understanding what the proximal pieces of the delivery are and what they look like when they fire efficiently is an essential piece of knowledge for a coach to understand in order to maximize the development of a pitcher's delivery. In future blogs, we will continue to look at research articles regarding how the body moves as well as discuss how to help train these segments of the body in pitchers.

Check out the research article for yourself:

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