In my last column, I brought up the way our shoulder evolved from weight bearing to a variety of other functions that require more dexterity, like manipulating tools and throwing for hunting.
The change in shoulder structure from a deep socket, stronger but less flexible structure into a more dexterous but weaker and shallower socket structure produced drawbacks as well as advantages.
Success requires that we throw with a high degree of accuracy and velocity and this requires a variety of abilities including the timing of the contributing segments of the body such as leg support, trunk rotation, shoulder movement, elbow extension and finally wrist and finger transfer of momentum to the ball. It is one of the most complex tasks that we can do and requires much practice.
Baseball and softball pitchers can repeat thousands of throws over a relatively short period of time during practices and games and the repetitive load on the weaker structures in this chain can lead to injury. The shoulder and elbow are particularly susceptible.
The load on the shoulder during an overhead baseball pitch is estimated to be at just over 100 per cent of body weight for compressive force and close to 50 per cent for shear force.
In order to create the greatest range of motion that will essentially ‘sling-shot’ the ball to the plate with the greatest speed, the shoulder is usually put in positions that load the passive, elastic structures (tendons, ligaments and capsule) as well as the muscles.
During the pitch, a number of structures can be compromised.
In the ‘cocking’ phase the head of the humerus (the ball of the upper arm) is pushed forward in the socket and the anterior capsule will be subjected to repeated loads. This may over time cause the capsule to stretch and become lax, further increasing the risk of injury. The ligaments and tendons in the anterior shoulder also take high loads and are also at risk.
During the mid portion of the pitch to the follow-through, the rotator cuff muscles are asked to contract forcibly in order to decelerate the arm from rotating at speeds of 7,000 to 9,000 degrees per second and to stabilize and resist distraction of the head of the humerus. While the arm is above the head, structures including the rotator cuff tendon can be compressed and pinched up against the acromion and clavicle bones (AC joint) causing an irritation, tendonitis and what’s called impingement. Repeated high forces coupled with fatigue and deteriorating biomechanics put the athlete at risk for injury.
One might think that since softball, or fast-pitch, delivers the ball while the shoulder is in a more stable low position, that might require less force be put on the shoulder and elbow – but that is not quite the case.
Forces measured during the windmill pitch were very near 100 per cent body weight, similar to that of the overhead pitch. During this pitch all the same muscles were firing at high levels, but the one that seems to have the most susceptibility to injury is the biceps. The biceps muscle multi-tasks to bring the arm forward to create the speed of the pitch, but also it is a main stabilizer of the shoulder.
The elbow is a hinge joint, but during a typical overhand baseball pitch it is asked to extend, but also resist opening up sideways while a terrific amount of force is placed on it. The force from the weight of the ball causes the lateral portion to be compressed and the medial part to open up. This opening is resisted by the ulnar collateral ligament. With repeated forceful pitches this ligament can stretch or tear which can result in what has been called “Tommy John” surgery (named for the pitcher who first had the procedure done to his elbow in 1974).
Prevention of these injuries is multi-faceted. Many variables need to be considered including strength, flexibility, technique, timing, physical maturity, previous injury and pitch-count. Pitch-count during practice and games is something coaches should be able to inform their athletes about. It is much better to pre-habilitate and prevent than to rehabilitate, so seek the proper help to avoid injury.
(Kerry Senchyna is the owner of West Coast Kinesiology and is a registered kinesiologist (BCAK).
