If you’ve ever watched a slow-motion video of a baseball player throw or a pitcher pitch from the mound it is an astonishing and fascinating sight.
The arm goes through positions that are unfathomable to most viewers.
It is amazing that pitchers can perform this motion and even more impressive that they can do it without hurting themselves. Of course, given enough time and repetition they can get injured.
In the last two to three million years of hominid history there were a number of developments that led to evolutionary success and the ability to throw was a key to survival while hunting. Archeologists have found that we became much more efficient carnivores during that period.
To investigate throwing we need to understand how the shoulder evolved. There are striking similarities between the shoulder and hip that demonstrate that both joints performed the same function at one point in our evolution – locomotion. These joints are comprised of identical structures.
When we began to walk upright, changes occurred that allowed us to become excellent long-distance runners. More flexibility developed between the pelvis and rib cage. This not only allowed for a more efficient running stride and breathing, but created the crucial ability to rotate the trunk, which is important in being able to throw forcefully and accurately.
The bones of the arm became smaller since they weren’t needed to support our body weight, and the shoulder girdle and its connection to our neck and collarbone became more flexible. This allowed us to use tools and throw with more dexterity, accuracy and power.
In nature we find that only primates have the ability to throw. Chimpanzees, for example, don’t throw specifically for accuracy and with much less velocity than humans. They seem only to throw for display and communication. They also use dart-throwing motion because they lack the changes in structure that humans developed.
Some of the key changes in shoulder structure include a shallower socket and the ability of the upper arm bone (humerus) to twist through a greater range-of-motion. There appears to have been a trade-off between size of the structures and flexibility. The smaller socket and bones allows greater range, but less area for muscle attachment. The ability to create more rotation of the humerus means that the tendons and support structures can provide more elastic contribution to the motion, but it leaves those structures open to tearing. The shoulder has been described not so much as a ball-and-socket joint, but like a golf ball and tee, where the golf ball is the head of the humerus and the socket is the tee. Not a strong structure for large forces, but excellent for throwing light objects accurately with high speeds.
The loading of the bones, muscles, tendons and ligaments can produce rotation speeds of up to 9,000 degrees per second in the humerus. This can produce pitching speeds of around 100-105 MPH in the best pitchers in the world, but the risk for injury is apparent at these velocities.
Next column I’ll discuss the overhand throw more in depth and compare it to underhand, windmill style of pitching used in fastball.
Kerry Senchyna is the founder, owner and president of West Coast Kinesiology.
