Hi Jared,
I think that the last study you referenced has some flaws that even an “educated layman” such as me can see which is that the only mattresses used for the study were Select Comfort air mattresses which have their own limitations, that all the subjects were tested in a side sleeping position only (without any consideration for rotational alignment or alignment in any other sleeping positions) and that the results were only based on a single study session that lasted for only 30 minutes and didn’t involve any actual sleeping. The goal of a study was to determine whether sub optimal spinal alignment would affect the subject’s ability to relax or initiate sleep but not to test for the effects of sustained alignment issues over the course of even a single night much less many nights in “real life” conditions.
There is also some evidence in this study that “self reporting” based on a subjective sense of “comfort” isn’t the most reliable way to assess sleep quality.
I think that the conclusion of the second study you referenced would be much more valid …
With or without studies, it would be clear to most people in any health profession that dealt with sleep issues or with back health that “neutral alignment” would be a significant factor in the quality of sleep and back health but if you are looking for more reference material then books such as “Back and Bed … Ergonomic Aspects of Sleeping by Bart Haex” (who was also involved in the second study you referenced) would provide plenty of evidence that alignment is the most important factor in the quality of sleep over time. You can see some excerpts from the book in post #2 here that talks about sleeping habits in different cultures. It is not an easy read because of some of the technical information and math it includes but the information that is included in it would be valuable for anyone regardless of their level of technical or mathematical knowledge.
Another book that would be well worth reading is “Preventive Biomechanics … Optimizing Support Systems for the Human Body in the Lying and Sitting Position by Gerhard Silber and Christophe Then”. It is more complex and would probably be a more difficult read yet but it also includes some great information for those that are interested in the more scientific aspects of sleeping posture and healthy sleeping.
Phoenix