Hi Beating Drum,
The erector spinae muscles are the ones that need to be relaxed in order for a chiropractor to work on you. The erector spinae (pronounced "e-wreck-tor spin aa") are actually a large group of muscles that originate on your ribs and insert into each of the vertebrae. Some of the fibers cross over only one rib and some travel over several ribs. The purpose of the muscles are to turn your vertebrae either to the right or left, and to pull you up from a bent position (hence the name "erect spine"). However, when the muscles go into a spasm (that's a long story on its own and you can read about it at Julstro - sports injuries, muscle pain, sports medicine
Go to the section titled "muscles and pain" and then "what's happening really") it's like having a tight rope with a knot in the middle, the muscle becomes shortened. As it shortens it places a great deal of pressure on the spine and pulls the vertebra in that direction.
If the tight muscle is pulling down, the vertebra is pulled down onto the disk and you will be told you have a compressed disk. If it's pulling hard on one side and not the other you can get a bulging disk, just as stepping on a jelly donut will cause the jelly to shoot out the opposite side from the pressure.
So, the solution. Lie on the floor and use a tennis ball. Put the ball to the right side of your spine -- definitely DON'T press on your spine, but instead have it on the muscle that is just to the right of the bones. Then bend your legs and begin to push with your feet. The ball will start to roll down your back, right next to the spine. As it does it will force toxins (lactic acid) from the muscle and draw blood into the muscle which will nourish the fibers.
As the lactic acid is released (again, too much to explain for this blog) the muscle relaxes and the strain is taken off the bone and disk. Push with your feet until the ball gets all the way to your posterior pelvis. Then go back up and put the ball on the left side of your vertebrae and do the same thing on the left side.
If your muscles are really tight you may have to rotate your body so you are leaning into the ball rather than lying right on top of it. You'll understand as you do the movement.
For the past 18 years I've worked with endurance athletes and people who have chronic pain.This treatment has worked for many hundreds of people all around the world. I believe it will work for you as well, just make sure you stay off your vertebrae and stay on the muscle, and if it's too painful just rest into the ball instead of being on top of it.
Wishing you well,