Not a doctor.

My core is plenty strong and limber.

A few years ago I built an upright bike that should have been extremely comfortable.

First test ride up and down the street confirmed that it was relaxed and comfy.

First long ride and I was in horrible pain. Hands, wrists, neck, shoulders, lower back, and crotch were killing me. I had to get off the bike every 2 miles just to make it home. I knew from my other bikes that the saddle was a good fit, at the right height, angle, and set back. It had upright bars that swept back a bit.

What the heck is wrong here I asked myself.

After riding the bike a few more times and analyzing my weight distribution I figured out what was wrong. I couldn't put my weight on my sit bones. Too much reach. I installed a shorter stem and every issue immediately disappeared. The bike went from literal torture rack to the leisure cruiser I had set out to build.