A couple of shoulder fatigue / soreness management tips for you - try these in the order that you start to feel any significant pain when you're swimming this weekend:
- check your stroke for a thumb-first hand entry and/or a midline cross-over as you enter into the water - the two leading causes of shoulder soreness in swimming! Hand entry should be finger-tips first and for the middle finger to be extending forwards in front of the same shoulder, not across. Watch this video clip on Saturday night (and now) for a great demo of how to do this properly: http://www.youtube.com/watch?v=s3HhNlysFDs&feature=youtu.be
- whichever shoulder starts to hurt first, breathe more frequently to that side for 15-20 minutes. This will force you to rotate better to that side and consequently reduce some of the pressure on that shoulder. Even just being conscious of rotating more to that side will help.
- when you have your paddler with you, let them do the navigating for you...you could do the whole 19.7km of not needing to sight at all if you have your paddler by your side and trust their judgement. Often times, repetitive lifting to sight (especially in rough water) can cause the shoulders to eventually feel pain because of the lift required to get your eyes above the water.
- try shortening the stroke just a smidgen and elevating the stroke rate just a touch...overly gliding especially when rough will leave your lead arm in too much of an extended position too long within the stroke and can in some cases cause pain when fatigue sets in. Whilst this isn't necessarily required in everyone's stroke, it won't do any harm to try it if the above two points haven't made much difference.
- try straightening the arm a touch during the recovery phase rather than aiming for the classic high elbow recovery - you don't need to swing the arm over the water, but just focus on loose shoulders and better mobilisation in the socket rather than forcing an artificially high elbow.
- in extreme cases (as I did in my 2009 swim) I had to open my left-hand fingers a touch during the pull through to take some load off during the propulsive phase of the stroke - of course I slowed down as a result of slipping my catch a little bit, but I did make it across.
- have your paddler carry some emergency ibuprofen with you if your shoulders are starting to get really sore.
...hopefully you'll all be OK, but most swimmers do experience some degree of shoulder fatigue / soreness in swims of this nature, so rather than being ignorant to this fact, the savvy swimmers takes an arsenal of tips to try with them to best manage these situations.
Hope this helps!