Hello Stephanie
Thanks for posting your question.
Firstly, I would love to ask your student what he meant by “difficult” and exactly where he felt any discomfort. Legs up the wall can cause tingling and pins and needle feelings in the legs for some students. Is this what he meant? (If so, he can bring his legs down into a Wall Squat or do a Reclining Twist until the feelings go away.) Legs up the wall can also create an uncomfortable stretch in the back of the legs (hamstrings) due to the hip flexion. Is that where he felt it? (If so, having a bolster or some support under the pelvis or moving his hips away from the walls may help.) Or was he experiencing pain or discomfort along the spine or in the back, as you seem to be indicating?
If the challenge was in the back, where? Upper back? Lower back? Neck?
For most students, lying on the back, whether doing Wall Yin or simply lying in Shavasana, tends to straighten the spine. Remember, a straight spine is not a neutral spine! (See
Your Spine, Your Yoga for an in depth investigation of this.) A fully straight spine has a maximally extended thoracic region and a fully flexed lumbar region. So, you are partly correct when you say “legs up the wall is a spinal extension”: it is only spinal extension for the thoracic spine. The lumbar spine will be flexed in this position. Again, where did he feel the challenge? Lower back, mid back, upper back?
Students with limitation to extension in the thoracic will often require a pillow under their head during Shavasana because their thoracic curve forces the head to be forward of the shoulders. Is this what your student is experiencing? Does he have some hyperkyphosis? If so, then I could understand this position being a challenge for him, and maybe he does need a pillow under his neck, or you could try raising his hips onto some support and see if that eases his thoracic extension. If he is feeling this as too much flexion in his lumbar, try reducing the amount of hip flexion in the pose by moving him a bit away from the wall or bending the knees.
There are many conditions that could make this pose challenging: hyperkyphosis, hypolordosis, bulging discs, spinal stenosis, etc. But rather than speculate, ask him to increase the granularity of his observation. What is he feeling? Where exactly? Can he describe it in more detail? Is it deep or superficial? Is it in one area or spread out? Does the sensation have a shape to it? Once you have this additional data, it will be easier to determine some possible causes of his discomfort. Once you know a cause, you can start to offer some alternatives to try out.
I hope this helps
Cheers
Bernie
