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Immediate Acceleration to Terminal Deceleration: How can 160 lbs produce 91 MPH?


This post will discuss how biomechanics principles can translate into a simple mantra to conceptualize movement.

We use the term “immediate acceleration to terminal deceleration” as a talking point for athletes and coaches to understand the mechanisms of a pitcher’s center of mass traveling down the mound, followed by a dead halt in said displacement. The theory continues to suggest that the next step in the sequence is channeling kinetic energy through the ground, up the body and into the ball. Though the term ‘immediate acceleration to terminal deceleration’ is not be completely sound from a kinematic or biomechanics perspective, thats not really the point. Many people have been able to grasp the overarching concept with the help of this term without focusing on specific mechanical cueing or adjusting a singular body part or movement- which is the goal.

Immediate Acceleration

Once the pitcher begins his leg lift, he has three options: to arrive at a traditional balance point, to begin drifting his center of mass toward the plate or to explode toward the plate (think more slide step). Immediate acceleration is not a cue for the pitcher to have a quick time to the plate, to slide step or to just move as quickly as possible.

However, immediate acceleration has everything to do with the acceleration of the pitcher’s center of mass and velocity towards the plate. If this is unclear, think of it this way: without context, immediate acceleration may sound like it cues the pitcher to rush to the plate and just move as fast as possible- this is not correct. With proper context, the pitcher can understand that at some point in the delivery, there is an explosion (moment of acceleration) towards the plate where his velocity rapidly increases propelling him towards his target. At that given

point [at the point of explosion], immediate acceleration takes place.

Note: for our purposes, moving a pitcher’s center of mass down the mound, refers to the displacement of his belly button from point A (above the rubber) to point B (down the slope). Understanding immediate acceleration should allow the pitcher to grasp the importance of increasing the acceleration phase of the delivery and his peak controlled velocity.

Terminal Deceleration: Two Methods

Strike Foot Stab

Terminal deceleration alludes to the phase of throwing known as “foot strike”. Consider this, with the increased velocity of the pitcher’s body moving toward the plate and the forces that are generated from those high-level speeds, the pitcher’s foot will then “stab” or “slam” into the ground applying immediate ground reaction forces against the direction of momentum and the throw. When the pitcher lands, his energy is initially moving down into the ground and towards the plate.

Zane Stephens: Mississippi State- 6’’0/ 160 lbs


Then, if the physiology of the pitchers calls for a “stab” like motion, his knee will land in flexion and transfer into extension (channeling that forward energy back up his leg into his torso and up through the arm) causing forward trunk flexion and a more efficient shoulder rotation, thereby yielding a more efficient and later unraveling of the elbow before ball release. Think of it like this, when the pitcher lands, his landing leg is in flexion and is in thoracic extension with all his intended energy and force going towards the plate. In this same phase, his lead leg will be stabbed into the ground and stopping his forward momentum. This momentum will be redirected into the ground, and channeled up his body through an extended leg. The leg will transfer the energy into the trunk cueing the athlete to begin shoulder rotation, forward trunk flexion and the acceleration phase of his throw. As his lower half works to decelerate his momentum, his upper half accepts the redirected energy to accelerate at peak force and velocity. Zane is a good example of this “foot strike stab” mechanism and it is just one reason why he is able to leverage high velocity despite having a smaller frame.

Leg Claw

The leg claw mechanism is similar to the ‘strike foot stab’ in that the goal is to accomplish a more efficient shoulder rotation and elbow unravel all due to the forward trunk flexion and redirection of energy. When a pitcher who employs this method lands, he is also in knee flexion. Yet, rather than getting to full knee extension as a by product or redirecting energy and forces, the function of the landing leg is to apply ground reaction forces down and backwards towards to second base, not just slamming down into the ground. Think of an elite sprinter gouging out the ground to pull himself forward with each foot strike. If the pitcher can effectively do the same, he allows for a better sequencing of movement. Notice Jamil Vanheyningen in the video below. Jamil is 6"6 230 pounds and up to 95 MPH at age 18.

Notice: Jamil's front leg action. Subtle in first angle, apparent in second.

Final Thoughts

This article is to serve as an overarching idea and not get too deep into the kinetics or biomechanics of the throw. Direction of applied force into the ground, duration of applied force, rotational angular velocities are all talks for another article. If you’d like to talk more on this front, please email us or DM on twitter. We’re always happy to talk.


The goal with understanding terminal deceleration is to conceptualize the conversion of energy and forces into the ground and channeling it up the kinetic chain while propelling the ball forward.

If the pitcher can conceptualize terminal deceleration, he can then visualize what this may look like in his own body and why it is beneficial. Everybody and every delivery is so unique and unlike any other. Allowing an athlete to take an idea and internalize it and then visualize the potential of his movements is an invaluable way to steals reps without getting on the mound.

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