For S1 root compression wheteher it is due to spinal stenosis caused by Wikipedia reference-linkfacet joint problems or due to the prolapse of intervertebral discs, try to remember these things. Flexion exercises of spine causes the unloading of the facet joints so relieve the spine from problems caused due to facet joint problems. On the other hand spinal extension exercises causes the unloading of the intervertebral discs, and so relieve the problems caused by intervertebral disc prolapse or degeneration,etc. So both spinal flexion and extension exercises will help to relieve the compression of S1 root caused by both facet and/or disc problems depending upon the nature of the cause. Try ultrasound therapy with continous mode paraspinal region to relieve the inflammation or oedema around the affected nerve sheath or nerve root to relieve the nerve ischemia caused by compression due to inflammation.

Williams flexion type of exercises will help best in stenosis of spine and of course of the nerve root compression. Advise the patient to do the bicycling and walking on a sloped treadmill to produce the flexion of the spine. In my opinion it will help you in clearing the problem of S1 root compression.