I would look to studies done by the physios at the Australian Institute of Sport. I think Popov did quite a bit of work down there. The availability of mobility in the thoracic cage would be of importance to allow a good deal of scapula movement. Restriction in that area will lead to impingement of both glenohumeral and cervical structures as well as possible elevation of the first and second rib joints.

One should also look at the training to ensure that backstrooke is also included in their training. This will assist to balance the spine. Unfortunately we have all seen swimmers standing on the blocks and they, like ski paddlers, have postures bordering on the frightening!