Shoulder dislocations are infrequent but are still the most common serious injury in kayaking. Most first time dislocations are related to poor form while performing a brace or a roll. To prevent this painful and hard to rehabilitate injury, keep your arms low and in front of your torso when performing a roll or brace. Slouching your back puts stress on the shoulder by reducing both boat stability and your rotation.
The weakest position for a shoulder:
This hitchhiking position is the weakest spot of the shoulder joint.
A better bracing position: elbows low, twisted to look at the blade.