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 allows humans to throw way harder than our closest relatives in the animal kingdom, the chimp.
The 3 traits are:
- Tall Mobile Waist – Long torso
- Less Humeral Torsion
- 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 retro-version 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 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. This picture below shows us the difference 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 is knuckles are almost hitting the dirt he is still showing 90 degrees of arm abduction
So we know now that humans have more laterally orientated GH joints but there is some variation within the human spices as to how laterally orientated the shoulder joint is for each person. This is going to be another case where I go back to the analogy of getting a suit tailored to your body rather than going with the standard “off the rack”.
Having a shirt that fits the slope of our shoulders is going to feel and look better. The same can be said about pitching mechanics. Maybe this has something to do with finding one’s “natural arm slot” since there does seem to be a little bit if wiggle room with that 90 degree angle rule in that you can be plus or minus 10 degrees.
Some people will naturally have either sloped or square shoulders but we don’t want it to be exaggerated by either tight traps pulling our shoulders up closer to our ears nor do we want tight lats pulling our shoulders down towards our toes. Either of these overactive muscles can increase the risk of injury while also decreasing performance.
Now that we know how these traits allow us as humans to take full advantage elastic energy we will learn exactly how this vital power source works in the shoulder and how it too will differ from person to person.
Graeme Lehman, MSc, CSCS