one armed drills

[Danny]

Today I started doing some one-armed free style to see if I could isolate problems and asymmetries in my stroke. Never really tried this before and a few things surprised me. First, with two arms my SPL for 25 m was about 18, but with one arm it dropped to 16 or sometimes even 15. Second it seems harder to use body rotation in my stroke when the other arm is always in front. As a result, I think I am working harder to swim this way. Needed to take a break every 25 m as a result. When I think about this on land, I don't see any reason why body rotation can't be used the same way with one arm as with two, but it didn't feel this way in the water. My guess is that my SPL dropped because somehow I have some disturbance in body position when I swim with two arms and by swimming with only one arm I was maintaining a better streamline. Any insights into this?

Also, is this a good way to study both sides of my stroke separately to look for asymmetries?