Recently, I have been experiencing pain in my left shoulder as a result of DNF training. I really love to do DNF, so I thought about it a bit, did a bit of experimentation, and came up with this modified armstroke.
The main focus of this change was to keep my arms in front of my body as much as possible during the first part of the stroke. Once the arms pass below eye level, and the arms are rotated outward, the stroke becomes pretty normal.
I do not expect this to solve all problems, but since I have made this change, I have had no pain at all in my shoulder. I might even be able to train with this stroke and compete using a more normal stroke. I am hoping that this will do a lot to preserve my shoulders.
In terms of performace, this stroke gets me down the pool just fine. I really do not notice much difference, if any, compared to a normal armstroke.
Another option would be to do the arm pull sequentially. Doing it this way eliminates the interference between your hands and arms if you do the arms together. Also, when you do it sequentially, the stroke becomes more and more llike a freestyle catch and pull. You just need to position your arms such that you go in a straight line. You end up with a kick - glide - first arm pull - glide - second arm pull - glide - arm recovery - and so on. I think I will call this the Sequential Hybrid DNF Armstroke, or Walt's DNF Armstroke, if you like. I have tested this briefly, but not in a regulation pool yet. It seems to work great. I think you might get more total power doing this than with a normal armstroke because you can use your entire core to power each arm pull independently, but it may be slower than the non-sequential way. I will need to test this in a regulation pool to really determine which way is best. I can see from the video that one thing I really need to work on is the early vertical forearm.
Here is a video during my first day doing this in a 25 meter pool. It is almost exactly the same speed as doing it non-sequentially, but the sequential method uses about one less stroke per 25 meters. I think this is because the hands stay out of each others' way on the arm pull, so maybe there is better power transfer and less unproductive turbulence. I obviously still have some work to do.
In this video I am wearing an old wetsuit bottom with the legs cut off and a silicone weight belt to hold it all together, as I forgot my swimsuit. I think a proper wetsuit, some work on timing, and a quicker turn will shave seconds off of these slow lap times. Stay tuned. The one huge advantage of all of this is that for me, it doesn't hurt.
One thing that has happened, after using this stroke for more than a month, is that my shoulder has healed up, and I am able to make a normal stroke again. I won't be using this stroke much anymore, but it was a great way to take stress off my shoulder for awhile.