This article is going to continue to look at how the human body was designed to take advantage of elastic energy and throw better than any other species on earth.  The previous article quickly touched on how this ability to throw played an important role in the evolution of the human species while going into great detail about one of three traits that allow humans to throw way harder than our closest relatives in the animal kingdom, the chimp.

The 3 traits are:

1. Tall Mobile Waist – Long torso
2. Less Humeral Torsion
3. Laterally Orientated Glenohumeral Joint

#2 – Less Humeral Torsion

Humeral torsion is a term used to describe the twisted shape of the humeral shaft.  You have probably heard of the term “retroversion” which is used to describe the same thing as humeral torsion, the only difference is the angle that you are measuring.

We want more retroversion and less torsion to create bigger ranges of motion.  Compared to chimps humans have 10-20 degrees less humeral torsion which allows for bigger ranges of motion like we see on the right.

Having larger amounts of external rotation has been shown to distinguish “fast” from “slow” throwers in previous research.  In 2001, Matsuo et al. published a study that reported harder throwers had 179 degrees of external rotation while the slower throwers were only able to demonstrate 166 degrees.

Here we can see Billy Wagner getting approx 180 of external rotation or “layback”, but we also have to consider the fact that he is going down the mound which makes this 180 closer to 200 which is why he was throwing 100 mph when it wasn’t as common as it is today.  The hard throwers in the study were only throwing about 85 mph.

Having more ROM when we go back into external rotation allows for more elastic energy to be stored and released as we transition to internal rotation during the acceleration phase.  When dealing with really fast movements, like throwing, elastic energy is what we want since it is made for speed whereas the power we get from muscles is designed more for moving heavy things at a slower rate.

The amount of torsion/retroversion that we have is determined partially by how much throwing that we do when we are young.  If we are able to keep our juvenile levels of torsion into adulthood we stand to benefit from this extra range of motion that naturally decreases as we age with what’s called anteversion.  To learn more read this great article by Eric Cressey called “Why Does President Obama Throw Like a Girl”

#3  – More Lateral Orientated Glenohumeral Joint

The glenohumeral joint (aka the shoulder) is classified as a ball and socket joint.  The “socket “portion is the glenoid fossa which is part of the scapula/shoulder blade while the “ball” is the head of the humerus.  In humans, this socket is facing to the side (aka laterally) while in chimps it is facing more upwards.  The picture below shows us the difference between the two with the human scapula on the left.

This does is creates a better angle to both produce and transfer force which is displayed in the picture below.  Having the arm abducted at 90 degrees from the body allows for more energy to be transferred from the rotating torso creating torque.  The approx 135-degree angle shown on the right from the chimp doesn’t allow for as much energy transfer from the torso when throwing but it is better for climbing, which for chimps is pretty important.  That’s evolution for you.

When the arm is at the 90-degree angle it puts the long axis of the humerus in line with the axis of the pectoralis major which acts as an internal rotator.  On the right in the picture below we see the muscle fibers of the human pectoralis major and how they run almost straight across at that 90-degree angle.

This really illustrates why we need to be near that 90-degree angle of arm abduction when we throw no matter if you throw “over the top”, “three-quarters”, “side arm” or even “submarine”.  Check out this article to learn more about this 90-degree rule and how throwing “over the top” increases velocity and stress on the arm.

Even if his knuckles are almost hitting the dirt he is still showing 90 degrees of arm abduction

Graeme Lehman, MSc, CSCS