Is The 3/4 Arm Slot A Myth?

I was going through my files last night and came across an article in which the author described the three different arm slots: overhand, 3/4, and sidearm. I had a couple of problems with this article that I wanted to share with the group.

The first problem that I had with the article is a small one; technically, I think there are four different arm slots…

  1. Overhand
  2. 3/4
  3. Sidearm
  4. Submarine

The bigger problem I had with the article was how it described the 3/4 arm slot. In the picture that accompanied the article, the author described the 3/4 arm slot as one in which the shoulders were horizontal, the pitching-arm-side (or “PAS”) upper arm was also horizontal (such that the PAS elbow was at the level of the shoulders), and the PAS forearm was vertical (with the PAS elbow bent 90 degrees).

The problem is that this isn’t an accurate description of the 3/4 arm slot because what was shown in the photo isn’t anatomically possible. There is no way for someone to throw (at speed) while keeping their PAS forearm vertical. Instead, as the shoulders start to turn, the PAS forearm bounces or lays back so that it is horizontal (but still level with the shoulders). The elbow then rapdily extends as the shoulders start to slow down. As a result, if their shoulders are level, then someone who thinks they are throwing from the 3/4 arm slot is actually throwing from what could be more accurately described as a sidearm arm slot.

The only way to actually throw from what could be described as a 3/4 slot is to tilt the shoulders 45 degrees.

All of this reflects what I think is a bigger problem with the state of the art of pitching instruction; I don’t think many pitching instructors really understand what the body does as the ball is thrown. As a result, they sometimes give advice to people that is out of touch with reality.

[quote=“Chris O’Leary”]…as the shoulders start to turn, the PAS forearm bounces or lays back so that it is horizontal (but still level with the shoulders). [/quote]You probably expected this but I maintain that it doesn’t “bounce”. It “loops” in a smooth manner.

Other than that, I agree.

[quote=“dm59”][quote=“Chris O’Leary”]…as the shoulders start to turn, the PAS forearm bounces or lays back so that it is horizontal (but still level with the shoulders).
[/quote]You probably expected this but I maintain that it doesn’t “bounce”. It “loops” in a smooth manner.

Other than that, I agree.[/quote]

Hi dm59,

I’ve seen high speed film of this (500 frames per second) and as the elbow leads through acceleration, the forearm and ball hand does in fact ‘bounce’ downward and backward, in relation to the elbow. The end of this ‘bounce’ when, biomechanically, there are no muscles available to flex the elbow is the point where UCL’s ultimately tear. What we have always thought the arm does is not really what happens.

Without high speed film it certainly appears that the loop you describe happens smoothly. Unfortunately, it doesn’t. Some pitchers, like Mark Prior, adopt an early hand position similar to how catchers are taught to throw and this exacerbates the bounce.

While I don’t currently have high speed film of traditional mechanics in my possession, I’d be happy to send you (or anyone else) a CD file of high speed film that shows another way to do this. All I ask is that you don’t post it to the web or otherwise disseminate it without my express approval. Send me a private message with your info and I’ll mail it promptly.


The bouncing process isn’t as bad relatively speaking; an average of 90 degree in 125 milliseconds (1/8 of a second). However, it may be enough to cause shoulder problems if the person’s shoulder bounces more than 90 degrees (due to their starting to turn their shoulders before their forearm is vertical).

However, I wouldn’t describe the elbow extending 90 to 135 degrees in 30 milliseconds to be smooth. That sounds pretty violent to me.

It also isn’t a loop per se. The elbow bounces back at an angle of 90 degrees and maintains that angle until the shoulders start to decelerate. It then rapidly extends. If it was truly a loop, then the elbow would be extending the whole time that it is bounced.

That rapid extending of the elbow causes the Olecranon to slam into its Fossa and, over time, decreases the depth of the Fossa and reduces the Range Of Motion of the elbow.


I appreciate your comments. My take on this is that “reverse forearm bounce” is a misnomer. The positive part of what’s coming out of this thread is that this motion is extremely stressful on both the shoulder and elbow. No big surprise there for anyone. I still maintain that the forearm does not “bounce” back, down and up again. I also maintain that the hand takes a path that loops. Yes, Chris, the motion is fast and puts much stress on the tissues in the shoulder and elbow but the extension of elbow, which anyone would agree does have the potential for stress on the involved tissues, has nothing to do with the term we’re speaking of here.

Chris, take another look at the slow motion Clemens clip when he was with Toronto. Although the 90 deg (or thereabouts, maybe more acute with Clemens) angle of the forearm to the humerus is maintained, the path the hand takes is a loop. This is due to the fact that the elbow is coming around as the shoulders turn. The ball is kind of “dragged” back, down, around and up and over toward release. This is the loop I speak of. The extension of the elbow does not happen until the shoulders have completely squared to the plate. Thus, the 90 deg. ± bend does not change until then. At least not in a significant amount.

If we want to talk about “bounce” happening somewhere in all of this, we would need to talk about the muscles and connective tissues of the rotator cuff and the elbow. They are put on stretch rapidly as you, Chris, have pointed out. The UCL takes on an enormous amount of stress in this, as does the rotator cuff muscles and tendons. The “stretch shortening cycle” (SSC) is at work here and actually is a key ingredient in the entire process. By way of generating power, the SSC is vital BUT it comes at a cost, or a risk, should I say.

So, I would agree that there may be “bounce” because of the SSC in these tissues but “reverse forearm bounce” implies that the forearm as a unit goes back and down, then hits a stopping point and “bounces” back up. This is the part I do not believe happens because of the “loop” that takes place. I think this loop is essential in doing a couple of things. It allows the arm action in the pitching motion to steadily increase in tempo so that there are no pause which kill energy transfer and also that it helps to mitigate (not completely eliminate) the stresses put on the rotator cuff.

In conclusion, the stretch shortening cycle for elbow and shoulder muscles and connective tissue, YES, forearm bouncing, NO. As always, my opinion based on observation and much discussion.

Thanks for the discussion guys. I hope that, as we resolve what I believe has become a semantic argument, that some understanding of the stressful nature of this motion is now a little clearer to those who haven’t studied as much as others.

I don’t think the forearm bounces back, down, and up. Rather, it just bounces back as the humerus externally rotates.

I agree.

I don’t believe the SSC has all that much to do at this point. It would if the humerus externally rotated with the elbow bent 90 degrees and then rapidly internally rotated with the elbow kept at the same 90 degrees. Then the rapid internal rotation would serve as a significant source of power. However, the fact that the forearm flies out limits how much power can be generated by the internal rotation of the Humerus since the hand ends up rotating pretty much on the axis of rotation of the Humerus.

In the process of bouncing, it isn’t actually the forearm that bears most of the stress. Rather, it is the upper arm that rapidly externally rotates and then comes to a quick stop in the shoulder socket. If this rapid external rotation happens hard enough, then I believe it can damage the labrum.

I believe the severity of the bounce, and the stress on the Labrum, will vary from person to person and depend on such things as whether the pitching arm side forearm is vertical at the moment the shoulders start to turn and the angle at which the elbow is bent.

Chris, the arm never stops moving even for a splitsecond.

Actually, the upper arm externally rotates (or “bounces”) to the limits of the shoulder joint and only starts to internally rotate a few tens of milliseconds later. It maintains this maximally externally rotated position for a brief period of time while the shoulders are turning.

Now this I can agree with. I think it’s obvious by now that we have a misnomer here when we use the term “reverse FOREARM bounce” and speaking of elbow issues as a result of it. The forearm may just be the outward, obvious thing that shows that the humerus is externally rotating. It’s just that the forearm isn’t really “bouncing”. Maybe the rotator cuff participates in a SSC event which is a risky proposition. Yes, the elbow (UCL in particular) takes on tremendous stresses during all of this. The forearm bouncing isn’t a great term for describing what we all agree on, that being that this motion is nasty on the rotator cuff and elbow.

What the “loop” does is 2 things. It’s a way of responding to the competing demands of power and safety within the traditional pitching mechanics methods, which have proven to be those that can result in very high velocities. This is the way that the pros walk that fine line. They want the power and don’t want the injuries. This arm action, generally, is the response. It’s not perfect, of course but it is the best way anyone has been able to come up with so far to optimize the results on those 2 fronts. Enter Mike Marshall’s talk. No proof. Lot’s of talk.

I’ll say it again. If Marshall can prove comparable velocities with reduced risk of injury, I’ll throw away everything I’ve ever said about pitching and move on over.

I agree.

It’s probably better characterized as Reverse Pitching Upper Arm Bounce. I don’t believe that the elbow reaches peak strain at the moment that the upper arm bounces. Rather, I believe that the point of peak strain on the elbow occurs when it is rapidly extending (or flying out) between 90 and 135 degrees. This puts a very dynamic, multi-dimensional shear load on the UCL.

The problem is that this isn’t a conscious action that pitchers actively do; in fact, most do not even know it’s happening. They think something else is going on.

Rather, it’s just what the parts of the body do as a result of the forces being imparted on them. First, the rapid rotation of the shoulders (which causes the upper arm to bounce) and then the just as rapid deceleration of the the shoulders (which causes the forearm to fly out toward 3B).

It turns out that it’s probably mechanically efficient. The problem is that is is also potentially very harmful.

You’re spot on there Chris. I don’t teach it to the kids I work with. I show it to them and get them to appreciate what’s really going on but I DON’T tell them to try to do it. I don’t want them to be thinking about this while they pitch. I teach them to have arm action and timing that causes it to happen when all of the pieces are put together effectively. I believe it’s important for them to know about it because they can then appreciate why the timing and arm action needs to be this way.