Owie! My poor back!

[Dogmama]

Are you accidentally rounding your back out when you try to "tuck" your tummy? You want to keep the nice arch (where your back goes in) in the lumbar spine while on your bike. Your back should look the same standing on the ground and riding on the bike. (Flex at the hips, not the lumbar spine!)

I agree 100%.

Additionally, if you concentrate on keeping that nice arch, you'll find that you push with your upper hams/lower glutes (you know - where the little butt sag begins? Or is that reserved for us over 50 crowd?) Otherwise, you might be using your lower back to push.

Don't push big gears. Get a cadence monitor & keep your cadence above 85 - preferably 90 - unless you're going up a steep hill. Pushing hard will always kill my back. If you're dipping forward with each pedal stroke, you need to change to an easier gear.

Here are a couple of heavenly stretches:

Sit in a low chair. Put your left ankle on top of your right knee. Bend forward. Great glute stretch. Switch.

Sit on the floor and put the soles of your feet together. Your legs should make a diamond shape. Lean forward. This is a nice lower back stretch.

If you still have problems, you might want to see an orthopedic surgeon, preferably a doc who specializes in spines, to rule out any curvature or disk problems. My spine doc who fused my neck said that lower back problems are common in cyclists. My physical therapist agreed. Both are cyclists.

BTW, I saw a chiro for my neck & he made it MUCH worse. I'm sure there are some good chiro's, but if you're really serious about riding, I'd see a regular MD. X-rays cannot pick up a lot of spine problems. Even MRI's miss some problems (it didn't show my disk implanting itself into my spinal cord - yikes!)
During the whole neck ordeal, I kept telling anybody who would listen that I only need to turn my neck to the left so that I can see oncoming traffic. Yes, I was the one who rode two weeks post surgery with the cervical collar still on. Not a good idea. But the cars really avoided me!