Hi Liz.
The estimate of the amount of force generated by the “superman pose” comes from the work of Stuart McGill. I don’t think he has ever studied Bow Pose, however, so I can only estimate what that would be like. In my opinion, as the hands are holding the feet and the posture is not maintained solely by contraction of the erector spinae muscles along the spine, there would be less compressive force on the vertebral bodies. There is probably more stress on the posterior parts of the vertebrae, however, due to the shape of the pose. Bow is a much deeper extension of the spine than Locust Pose so there is more likelihood of compression being placed on the spinous processes and facet joints. Now, more is not necessary bad in this case: it depends. Even the force of 6,000 newtons is not necessarily bad — IF the students' spines have been trained to tolerate this much stress. For professional gymnasts, this is likely not a problem. For an untrained yoga student, this could be way too much. It depends upon the person’s biography and biology. How to tell? I don’t really know other than to ask the student what they are feeling in their backs while they do the pose, when they come out and over the next day or two. Is there pain or discomfort? If so, it is better to back off and do core strengthening work via McGill’s Big three exercises as described in my book Your Spine, Your Yoga.
Regarding placement of the feet in Prasarita Padottanasana (PP) — the right position is very individual. No aesthetic cue of “feet out” or “feet parallel” is going to work for every body. It depends upon the amount of tibial torsion the student has, the amount of femoral torsion and acetabular anteversion. And, yes, the cause of the sciatic is very important too. For discogenic sciatica, flexion of the lumbar as occurs in PP could be the problem. For piriformis caused sciatica, flexion, adduction and some internal rotation may trigger it. But, how do you know if someone’s legs are internally rotated? Looking at the feet will not tell you. At the end of the day, the best test of whether PP is okay for someone’s sciatica is to test it. Is sciatica made worse or better with different foot alignments? Is it better to not do the post at all?
The student has to be the one telling the teacher what works, not vice versa. Teachers can only make suggestions, teachers should not make diagnoses.
Cheers
Bernie
