Repeated throwing in sports such as baseball and cricket can place a large amount of stress on both the shoulder and the elbow. It is important for throwers/pitchers/bowlers to understand the different phases of throwing, to get a better idea of what structures are involved. Players that throw repetitively need to be able to have good strength and endurance in the muscles that stabilise the shoulder (rotator cuff), whilst also having good shoulder blade control. The four phases of throwing are:
- Wind up (preparation)
The wind-up phase establishes the rhythm of the throw, where the body rotates so that the hip and shoulders are at 90 degrees to the target. The lower leg is raised to help transfer energy from the legs to the upper body. In regards to the shoulder muscles, relatively little muscle activation occurs compared to the lower half of the body during this first phase.
During the cocking phase the body is now positioned in a way to utilise both the shoulder and the lower body to propel the ball forward. The upper arm is set away and behind the body, which creates a large elastic force in the shoulder capsule, ready for the acceleration phase. This phase of the throw places the shoulder in a compromised position, where people with shoulder instability become more susceptible to injury. The cocking phase ends with landing the leg down which transfers the energy from the lower body to the upper body.
The acceleration phase is extremely explosive; it uses the stored elastic energy from your shoulder capsule as well as the contraction of your shoulder internal rotators to propel the ball. This creates a large force at the shoulder joint, and thus activates the rotator cuff muscles (stabilisers) to help create stability within the joint. The acceleration phase concludes with the ball release, which occurs at approximately ear level.
After the ball has been released the rotator cuff muscles (stabilisers) now eccentrically contract to slow the arm down as it crosses the body. The rotator cuff muscles (stabilisers) are susceptible to injury in this phase as the muscles attempt to decelerate the arm. If the muscles become fatigued, due to poor endurance, majority of the force will be taken up by the shoulder joint.
Based on these four stages we can see the importance of our rotator cuff muscles. They not only help produce the force required for the throw but they also work to stabilise the joint and also slow the arm at the end of the throwing action. If these muscles are weak or fatigue early, more force will be placed onto the passive structures of the shoulder joint, increasing the chance of injury.
In order to prevent injury, it is important for throwers/pitchers/bowlers to incorporate a proper rotator cuff strengthening program. Another strategy to prevent injury can also be to tape the shoulder in a less compromised position, giving the shoulder more stability during the throw.
Some of these rotator cuff strengthening exercises can be found here.