Ok, so you love tennis. Or cricket. Baseball? If you play a sport that involves either throwing a ball or racquet, try this little experiment. Take your throwing arm or racquet arm and see how far you can reach behind your back (from below). Now try this with your other arm. Any difference?
If you are able to reach your non-throwing arm significantly further up your back than the other side, you may be suffering from glenohumeral internal rotation deficit (GIRD). GIRD is a condition that leads to the loss of internal rotation in shoulder joint (the movement that allows you to put your hand behind your back). Lets look at a little shoulder anatomy and biomechanics.
The shoulder joint is surrounded by a thin layer of tissue called capsule. The capsule is responsible for sealing the joint space, providing stability by limiting movements. It also helps with our joint position awareness and proprioception. When we put our shoulder through repetitive throwing motions over a long period of time, our capsule is distorted, leading to GIRD.
To understand why this happens better, lets look at what happens during a tennis serving motion.
Kinetic chain theory
The tennis serve is a kinetic chain which has five different phases:
1. Wind up (knee flexion, trunk rotation)
2. Early cocking
3. Late cocking
4. Acceleration phase (including long axis rotation)
5. Follow through
During phase 2 and 3 of the serve (as demonstrated by the red rectangle), our shoulder is in a position of maximal abduction and external rotation. It is this position that causes the front (anterior) portion of the capsule to stretch, whilst the back (posterior) becomes tighter. This posterior capsule tightness is what eventually restricts our movement.
Why does GIRD matter?
You may be thinking ok, so what if I can’t get my hand behind my back? If anything, you may have greater external rotation (movement in the opposite direction) with your throwing arm which makes you more flexible, right?
Unfortunately, that's not how it works. If you suffer from GIRD, you are at a higher risk of injuring your shoulder in the long run. If the limitation of internal rotation exceeds the gain you may get in external rotation, there is a decrease in your rotational arc. This leaves the shoulder is susceptible to injury. Some studies suggest you are 25% more likely to suffer from a tear to the cartilage in the shoulder, or a SLAP tear. Also, there is more chance of developing instability and impingement symptoms in the shoulder
The sleeper stretch
If you think you suffer from GIRD, don’t despair. First principles are always keep your shoulders, back and core muscles well balanced with conditioning and strength work. Avoid over loading one particular side of your body without working on the other side too. For example, when we throw, the muscles of our rotator cuff that help us internally rotate our shoulder become very strong, so be sure to work on the external rotatorstoo. They can easily be isolated using the cable machine in the gym. Also, working on technique to minimise injury is vital. By using the whole kinetic chain when throwing, we use the bigger muscles in our legs and torso to generate power rather than the shoulder.
There are basic stretches you can do to improve the loss of internal rotation. The first is to practice trying putting your hand behind your back and reaching as far up as you can. Try getting into the habit of doing this regularly, for example in the shower.
You are 25% more likely to suffer a cartilage tear in your shoulder if you suffer from GIRD
The sleeper stretch is a specific exercise that works on increasing the amount of internal rotation of the shoulder. Here is a brief description of how to do it (see diagram above).
Keep a measure of how your internal rotation movement improves by seeing how far you can get it up your back. Ideally, you want both sides to be the same.
I hope this blog has introduced the concept of GIRD to you. Remember, it is always important to accompany your chosen sport with strength and flexibility work. This will keep you playing injury free for longer!!