I have an Irving (GQ) parachute and one of the optional extras with the
chute is an inflatable lumbar pad which fits onto velcro strips on the
parachute back. The beauty of the system is that you can fit the pad in
exactly the right place and it won't move or get dislodged. It is
inflated using the squeeze bulb used on blood pressure monitors. Works a
treat.
I had an injury many years back to the lumbar 4/5 joint which causes pain
to the sciatic nerve. I have discovered over the years that the worst
thing you can do is keep still. The only thing I won't do while the pain
is severe is fly.