I certainly empathize. As one who was very fit up to the age of 60, lower back pain stopped me running…even on a soft beach. I can still cycle, but this does not compare to the stresses caused by running, even when pushing hard uphill.
I don’t like the sound of the alternative, so I wonder if the medics would allow you to support some of your weight on the side rails. I find that this helps, and still sends my heart-rate up much more than cycling. You would of course have to practice this for some time before submitting to a test.
The problem would be, how to factor this into their calculations. They surely factor for age…don’t they? ( I never had to do this test) so could some support be taken into account?
Do you get immediate pain--when running--as the result of the bulging disc? So many people have discs that are pushing right onto the spinal cord…and they never know.