Internal rotation of the shoulder on entry
Like others have mentioned the thumbs first entry needs to be avoided to protect your shoulder joint while swimming. At a squad recently there were 7 of us in the water and 4 reported some shoulder soreness. As a physiotherapist and TI coach you need to focus on preventation as your firrst option. Next time you swim,focus intensely on how your hands enter the water,a relaxed hand and arm with the middle finger entering the water first is the key to shoulder protection. A thumb first entry means the
arm bone has rotated on its long axis inwards towards the body and this causes compression of the soft tissues of the shoulder under the bony arch formed by the clavicle bone in front of your chest and the spine of your shoulder blade from the back. Lifting the elbow too high in the swing phase instead of the swing out recommended with TI is another potential cause of shoulder pain.