Odd technique variations during long piece

[zenpharaohs]

I was rowing a marathon at my long distance pace today, and after about 8km I got some tightness in my shoulders but I continued rowing underhand for a few km. It put my shoulders in a much stronger position, and changed the active muscles over which sort of gave me a new lease on fatigue. It had another interesting effect - it put my back in a stronger position and that helped too.

As I got in about 17km I found something else out - by tilting back quite a ways, I could convert the rowing motion from something close to a squat into something closer to a deadlift, and it also changes over to more of a decline row and this was a lot easier on my back. Previously, I had always tried to catch well upright, so this sort of angle was only possible with a large rockover which was fatiguing. I did this for about 2km and then went back to a more normal stroke. Then I got interrupted (see other thread). I was maintaining my pace (about 2:20 / 500) at a stroke rate of about 11 - 12 strokes per minute.

This is in pretty stark contrast to when I am rowing at a pace for a shorter distance - I tend to like a completely consistent form for 10k or less. I would have just gutted stuff out if I was going for 10k, but I was planning on a marathon, so I was thinking about staying comfortable.

Does anyone else mess around with form during long distances?