Several things might be causing back strain. Here is a list of possibilities:

- The sink should have 3-4" of countertop in front of it, not more. If the sink is installed too far back you have to bend more to work at the sink. Some people like an apron front sink for this reason - their bodies are directly up against the sink.

- if you have a high-arch pull-down faucet and the faucet is quite close to the rear of the sink. It means you will be bending and reaching slightly to be rinsing under the faucet. A pull-out faucet instead reaches several inches more into the center of the sink, so you don't have to reach as far to rinse things under a pull-out.

- if you are very tall, you have to bend more than a shorter person to reach to the bottom of the sink.

- if you have a tile floor which is hard on some people's backs.

Those are all just different possibilities - hard to know what it is exactly for you without knowing your specific set-up. You could try one of those cushy-mats for the floor for standing in front of the sink.

Everywhere I have to stand for long periods in my kitchen I have a Gel Pro mat which has really helped my back and legs.
I have one at my sink, baking station, and in front of my cooktop.
Since the home we bought came with custom tile flooring which I think is brutal on the back having these mats has made all the difference.
Hope this helps.

Check the reach of your faucet and the spout height. Sounds like it may be too far back or too low for you. I am a strong believer that the faucet is often more to blame than the sink.

Yeah, I think it may be the faucet. I have a Hans Grohe Talis S, which is a high arc one. I couldn't figure out why people wanted a pull-out. Now I know.

I did get some gel mats, and those seem to help a bit - we have porcelain floors, which are particularly hard on the body.

The sink is 4" back - I asked for it to be as close as possible to the front - our GC doesn't always listen, but at least it's in the range of comfort.

It's a bit too soon since the reno (literally days) to replace the faucet, but I'll keep an eye on where my hands are - maybe in a few months if it doesn't improve. FYI, we did get the Tapmaster, so at least I'm not always having to bend to turn faucet on and off.

THANKS all! and if anyone else has ideas, let me know.

You could also try putting a grid (or cutting board) into the bottom of the sink to make it higher -- sink might be too deep?

I second circuspeanut's grid suggestion. I'm not terribly tall at 5'8" but my grid has alleviated strain by taking away an inch of depth.

Yes, I did put the grid, I think the problem is the grid and the mat are canceling each other out. I am not terribly tall at 5'5". I think it really is the faucet and I'll have to watch how I stand. All in all, not a bad thing. I had an older friend who use to tell me, Boobs up - I'll have to remember it at the sink!

I'm 5'10 and got an 8" undermounted sink so its 9" deep. My previous sink was only 6" I think, so the 3" was a big change. My back does get sore after awhile leaning over it, and it didn't happen to me before. I definitely couldn't go deeper than what I have now, even though a 10" sounds heavenly!