Baseball Pitching-Arm Safety starts in the legs and trunk


Over the years many have claimed to have the ultimate, or absolute, answers in search of the perfect approach for delivering a pitch in baseball.  The problem is that there has been a fairly wide difference opinion and very little in evidence for support. 

I joined the crowd several years ago when Tim Lincecum was a student at the University of Washington and being considered for the draft. Several of the local scouts were skeptical of his mechanics and felt he would break down. Others expressed that, because he threw so hard, and was so good, he was worth a chance.  Several expressed the question as to how a guy his size threw so hard?

Because both ideas tweaked my interest as questions worthy of pursuit, I contacted Ken Knutson, the Washington coach at the time, and asked for video of his mechanics.  Because he was such a high profile prospect, there were plenty, but one face side and behind the catcher synced in unison proved helpful. I organized my questions and consulted, Dr. Mont Hubbard, then a mechanical and aeronautical engineering professor at U.C. Davis, where I was at the time the Head Coach.  Mont said he wasn’t more than a fan, but it would be interesting to work around my questions.  

At the time we, mostly Mont, concluded that he was very efficient, and that there were few points in his mechanics that would cause injury.  From my prospective as a coach, with concerns from a competitive view, as well as for injury, our long discussions raised a host of questions. But, the intriguing one for me was the possibility of measuring movement in the video to quantify the forces, isolate high stress points, and identify the mechanics that are stressful? So, from this prospective, let’s take a look.  

During my time attending clinics and participating in numerous discussions, I’ve been exposed to a wide range of ideas about the mechanics necessary to accelerate the baseball. 

The ideas include, tall and fall, sit and drive, extend or flex the lead knee, rotate the shoulders and hips as much as controllable, and don’t over rotate the shoulders and hips. In reality most mechanics in use combine, to some extent, most of the above. The question is: Is one more efficient in transferring momentum through the trunk and arm to accelerate hand speed, and if so why?

Let’s start with a couple of basic physics principles. Momentum is the product of mass and velocity. Momentum continues on a straight line unless it is altered by another force. For every action, there is an equal and opposite reaction. And, maybe the most important point is, the force to change directions is proportional to the speed and direction of momentum change. 

Since there is a fixed amount force available, any energy used to change directions is energy lost to accelerate the baseball.

Because I started this process with Lincecum, a smaller guy who threw hard, and I have fairly good video, I’ll use him here as an example. 

In the sequence below, the difference in distance covered between frame 2 and 3 is due mostly to gravity, and the distance between frames 3 and 6 are sit and drive. Between the 3 to 6 he covers about 4 times the distance in 1/3 the time as between 1 and 2. His push off from the rubber from this near seated position allows him to apply almost 90% of his energy toward the target.  The other 10%, or so, is directed up to balance the fall produced by gravity. This balance keeps his center of mass is moving horizontally, thus maximizing his efficiency. 

The advantage of this drop and drive is two fold, it utilizes leg muscles to produce momentum, and it facilitates directing the momentum toward the target.

This face side sequence of a young Lincecum working from a full windup is the example.

 He begins the movement forward by walking forward with his left foot to shift his center of mass forward and begins to fall and sit to almost to 90 degrees. This gets his leg almost to horizontal enabling him to create near maximum efficiency when he extends the knee to accelerate toward foot plant. 

It should be noted, that there is an advantage of his walking forward and falling to the seated position because he creates forward momentum as he moves over the rubber and falls to the seated position. This is an advantage because when he begins to extend his knee, the inertia created by the fall is added to that created by the leg drive.

Mr. Lincecum, using these mechanics was able to generate enough force forward to create one of the fastest and longest strides, as related to body height, of all pitchers in the game.  

So, one  of the reasons he threw so hard is that he created, relatively speaking, a tremendous amount of momentum moving to foot strike. This is significant, but transferring that linier momentum is really the key.

Keep in mind that the physicists tell us that an object in motion goes in a straight line unless its obstructed by another force. Here, the other force available is the foot plant. This is all well and good, but if the center of mass is directed directly at foot strike it will, if the opposing force is great enough, stop. As an analogy, imagine a car running into a tree. If it hits the tree exactly head on, the center of mass is directed directly at the tree. The headlights will fold toward each other, and there will be no rotation. On the other hand, If you move the contact point toward the edge of the car, the center of mass is directed away from the tree, the tree then becomes a pivot point, and the car will, on contact, begin to rotate at a rate relative to the distance away from the tree. 

The same is true for our pitcher.  If the momentum generated by our pitcher reaches foot strike with the center of mass directed directly at foot strike ,there will be little transfer producing rotation. If there is to be rotation, the momentum must be directed a way from foot plant, and, the greater the distance, the greater the rotation. 

To see how Mr. Lincecum accomplished moving the direction of his center of mass outside his foot plant, let’s check from another angle.

Example 1 

From here we see that he extends his stride knee and swings his fairly straight leg on a wide arc to foot plant. What this does is move his center of mass toward his lead foot. He also turns his shoulders to about 45 degrees from the target and begins rotating the shoulders and hips.  The effect is that at foot strike the energy from the legs is creating rotation of the trunk and shoulders. The analogy here we can use is a bouncing basketball. If you drop the ball with no spin, it comes straight back. If you spin the ball to the floor, it will bounce in the direction of the spin.  The result is that you can add this momentum to that created by the hips and trunk after foot strike.

What he has accomplished with this rotation is two fold. The extended leg moves the center of mass toward the throwing side, and the rotation created acts like the spinning basketball moving, in this example, toward the target.  These forces both contribute to the momentum transfer.

Another point to note is the angle of approach to foot plant. His stride leg remains extended away from his line to target creating a wide angle, 75-80 degrees, to foot plant. The reaction forces from this approach, equal and opposite, contribute to the rotation in two ways. The delay in direction change forces a greater acceleration and the reaction forces accelerate the shoulder turn.  The hight of his foot path is fairly low, but maintaining the height contributes  to the alignment of forces we will consider later. 

Another significant point, and maybe the frosting that made Mr. Lincecum so effective,is demonstrated here. He reaches foot plant with his knee flexed. He then extends the knee joint to force the left hip back, a move that accelerates the hip rotation. Most discussions that address hip rotation center around forcing the back hip forward, but this move works much like cracking a whip. It adds as long as the force is pushing the hip back and not up.  

Example 2 is a contrast

The disadvantages of the drop and drive are that an object falling at an acceleration rate of 32.16 feet per second, doesn’t have sufficient falling distance to create a comparable speed.

Another is, the momentum is angled down reducing the momentum efficiency by the difference in the angle from horizontal.

This example is pretty much the other end of the spectrum. The stride knee is flexed and takes a relatively straight path to foot plant. The hips rotate some, early, but soon open and have little rotation from the third frame to foot plant.  This approach keeps the center of mass moving closer to the pivot point with less leverage for momentum transfer for rotation. In the previous analogy the car is hitting the tree closer to the hood ornament. Thus, the momentum transfer is relatively less. 

Also note that the shorter route to foot plant takes less time, a point we will consider when discussing arm mechanics.

We also see a difference in the rotation. In this example a line from shoulder to shoulder and hip to hip and arrives at foot plant with little or no rotation. In the example 1 above there is almost 40 degrees rotation.

Example 3, Another version of Drop and Drive

Aroldis Chapman takes advantage of the extended leg and wide arc to footprint in a different manner than Lincecum.  He sits to near 90 degrees, extends the stride leg and approaches foot plant from a very wide angle, but stays on the pivot side longer.  This enables him to create hip rotation by driving his left hip forward against the resistance provided by the foot plant. Lincecum, on the other hand, creates the rotation by resisting the momentum created earlier in the process. They both create a high degree of transferrable momentum, but do it in a different manner.

Another important point to note is that, in order to throw hard, there is one checkpoint that is consistent.  

 All three reach foot plant with significant difference in the angle between the hips and shoulders. Golfers have made this an issue and call it the X factor. The idea is that you stretch the rotational muscles in the trunk to a position of maximum potential for a long and late acceleration. 

The question now is, WHAT DIFFERENCE DOES IT MAKE?

1. For a given amount of arm speed, the drop and drive with the pivot leg extended promotes greater transfer of momentum which in turn helps create greater speed with less stress.

2. The extended leg and wide angle of approach to foot plant takes longer, giving the arm more time for a longer and smoother acceleration, which is the topic of the next post. 

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