To Pronate Or Not To Pronate, Part 2

baseballthinktank Featured Post, Pitching Mechanics

All motioned with the strongest joynts performe
Lett the weaker second and perfect the same
The stronger joynt its motion first must end
Before the nixt to move in the least intend


(Written by T. Kinkaid in 1687 referring to the golf stroke)

In case you missed it, here is Part 1.

This little verse came from Kinetics of Human Motion by Vladimir M. Zatsiorsky.  Regarding the above verse Zatsiorsky writes;

This performance is known as the whip like movement. It is broadly used in throwing activities; during the delivery phase, acceleration and subsequent deceleration of body segments occur in a proximal-to-distal direction. The proximal-to-distal progression of limb motion in throwing and striking was known to practitioners well before scientific investigation of these activities began.

I used to hear quite often that throwing a baseball was all about arm strength and/or arm quickness. Nothing could be further from the truth or should I say facts.

Throwing is about developing momentum and then converting that momentum in such a manner as to accelerate a baseball.

 The primary mechanism for converting momentum is best illustrated by the comparison of a simple compound pendulum to a complex/compound pendulum.

  •  In its basic form the simple compound pendulum is simply a slender rod attached to one end and allowed to swing back and forth.
  • The complex compound pendulum is composed of segments where each segment is free to pivot around it and point

For the sake of illustration I am representing the simple compound pendulum as a series of solid links that rigidly connect three masses (weights) together to form a single rod which pivots around one point.

Figure 1

I create a second pendulum in this case a complex compound pendulum by connecting three masses with rope or some other very flexible material.

  • By connecting each mass with a flexible material it allows each mass move and rotate freely yet all of the masses are still held together by the rope.
  • In essence the simple compound pendulum becomes a complex compound pendulum.


Figure 2

 Taking both pendulums and displacing them 90° with respect to the vertical and allowing them to drop under the attraction of gravity,

the whip affect can be seen in the difference between endpoint velocities of the two pendulums.


 Figure 3: Endpoint velocity of simple compound pendulum = 29 feet/second

Endpoint velocity of complex compound pendulum = 66 feet/second


The main point I’m trying to make here is that it’s rotation around a fixed point creates velocity in throwing a baseball.

  • Rotating around a fixed point is about curvilinear motion i.e. were not talking about straight lines here.

Another absolutely critical concept that Marshall either totally dismisses or does not understand is the conservation of momentum.

Rotational momentum is most efficiently captured and transferred from one segment to the next if the next segment rotates in the same plane as the preceding segment that is transferring the momentum.

This is best illustrated by the following illustrations:


 Figure 4 The sequential buildup and transfer of rotational momentum

Figure 5 Matching the plane of the arm to the plane of rotational momentum

 Another extremely important point is that the angle of the joints is critical with respect to optimizing the throwing of the baseball. For example the amount of elbow flex prior to external rotation has a significant effect on not ball velocity but also ball movement. I’ll say this topic for another day.

From Coaching Pitchers By Michael G. Marshall, Ph.D. Chapter 29: Sir Isaac Newton

 Once baseball pitchers remove baseballs from their glove, the baseballs want to move at constant velocities in straight lines.  Therefore, if baseball pitchers want to move baseballs in non-straight lines, then they must apply additional force to overcome the straight-line inertial pathways baseballs want to follow.  To constantly have to overcome non-straight line movements wastes force.


     Curvilinear force applications waste force in two ways. 

  • First, they require pitchers to constantly redirect the mass of the baseballs. 
  • Second, they take force away from straight-line force applications.

      When baseball pitchers apply force from side-to-side and up-and-down as well as toward-home-plate, only the toward-home-plate force application influences release velocity.


Figure 6 Jeff Sparks illustrates Mike Marshall’s throwing mechanics:

Q:   Why am I picking Dr. Marshall?

A:  First of all I’m not picking on Dr. Marshall. What I am trying to do is develop a better understanding of where the current pronation fad came from. Dr. Marshall is, my opinion, the originator of pronation teaching. Understanding how he views how the body throws the baseball is critical to the discussion.

Understanding how the body REALLY throws the baseball IS THE prerequisite for understanding the how and why of pronation.

I’ve spent many (too many?) years and countless hours trying to understand the mechanics of throwing. Simulating the throwing motion using models based on physics has greatly increased my understanding of the throwing process.

This model is composed exclusively of a complex compound pendulum consisting of upper arm, forearm, and hand connected by what would be the shoulder joint, the elbow joint and the wrist joint.


Figure 7

  • The complex compound pendulum is attached by the shoulder joint to a mass which represents the upper torso.
  • The upper torso is rotated in such a manner to represent shoulder rotation using shoulder rotational velocities of an average college pitcher.

 This simulation results and a throwing velocity of 86 mph.

 In chapter 36 of Dr. Mike Marshall’s pitching book

 For pitchers to powerfully drive their pitches toward home plate, they need to strengthen the bones, ligaments and tendons of the muscles that accelerate their pitching arm toward home plate.   My mioanglos iron ball interval-training program increases the strength of these structures to withstand greater stress.

My pitchers start with six pound shot puts.   In size, six pound iron balls compare with softballs.   Therefore, while six pound iron balls require extra gripping effort, that extra gripping effort strengthens their ability to grip baseballs.

I’m not sure if the belief in arm strength is as dominant today as it was 10 or 15 years ago i.e. that the key to throwing hard is arm strength.

  1. How many times we seen the skinny kid throw bullets and the big muscular husky kid throw cream puffs?
  2. What exactly is arm strength?
  3. Is throwing a baseball caused by the effect of muscles contracting rapidly (strongly) to accelerate the baseball?
  4. Or is arm strength simply the strength necessary to withstand the inertial forces created by a whip like throwing action?

 Dr. Marshall (and many others?) believe that arm strength is necessary to actively accelerate the baseball.

 In the beginning I was just as guilty and believing arm strength with the key to throwing velocity. For example that the action of the triceps muscle is critical to extending the forearm to throw the baseball. Early in my throwing research I discovered a very interesting research paper which stated the following (and was the beginning of my throwing the baseball re-education)

Another study utilized a model to fractionate the three- dimensional angular acceleration vector of the segments during an overhand throw into the two-dimensional kinetic and kinematic parameters (Feltner, 1989). The results of this computer model revealed that the elbow extensor muscles created no extension moment as the distal segment began its rapid extension, suggesting that the inertial component of this joint action was the responsible agent for elbow extension. 


While Feltner was the first to propose that the elbow extensors did not contribute substantially to elbow extension during the overhand throw, it was not until Dobbins (Roberts, 1971) who, through the use of a differential radial nerve block to eliminate triceps activity, was able to provide substantive proof. Dobbins reported that after six practice trials, the participants were able to throw at greater than 85% of the velocity attained before the nerve block. These findings give credence to Feltner’s suggestion of the relative lack of contribution of the elbow extensor muscles during the rapid elbow extension during the overhand throw.

 The notion that the elbow extensors sparsely contribute to elbow extension in the overhand throw was further supported by two other groups, who reported very little elbow extensor activity during th e rapid elbow extension using EMG analysis (Toyoshima et al., 1976; Atwater, 1979; Fleisig et al., 1995), each supporting the inertial based Theory One (Ford, 1998).

 Again I ask the question “what is the role of arm strength in throwing a baseball”?

 Is it active participation the form of aggressive muscle contraction?

Or is it simply “holding on for dear life”?

Similar to a chain of ice skaters holding hands and skating rapidly in unison and then one end of the chain of skaters comes to a quick stop and the next skater comes to a stop and as the sequence progresses the last gators on the end furthest from the first data who stopped has everything to do to hold on and in most instances goes flying off in a straight line.

The biomechanical model shown in Figure 7 has no components that contract (shorten or stretch).

  • It is simply a series 3 slender rods (upper arm, forearm and hand) that are held in place with fixed (rigid) rods.
  • At the right time each rod is released i.e. the connection to the rod is broken so that the segment may then move on its own. The end result is a 86 miles an hour fastball.

Next time the anatomy of pronation.