Only tangentially related - I suffered from anerobic sensations in my torso as well as back pain climbing my fix gear for about 5 years. I'd run into this before though never on my racing bike. I started thinking the cause might be the high handlebar location caused by a laid back touring frame geometry and a very long head tube. So, not wanting to go to a track style dropping stem (this was before threadless was very far along), I had a horizontal quill stem made that would locate the handlebars so my shoulders could be in the position of that old racing bike. Since the bars had to be much higher, I compensated by designing a stem that was much longer. Had a local framebuilder make it. 180 mm long. Second ride was a very hilly 75 miles. No back pain. Felt great the whole ride, just very tired.

That thinking has made its way to all my bikes now. For me, a bike fits when I can stretch like a cat and make my back really long. Helps my spine, my lung capacity, the ability to diaphragm breath big time and feels like I am oxygenating my whole body when I do it.

Don't copy me on the stem length, I have arms that go horizon to horizon. But consider a trying stem that gives you far more reach and stretch than you currently have.

Ben