Unfortunately, I don't have the time to post as much as I used to...in order to better understand the physiologic and scientific basis of manual treatment you need to get away from "brand-names" such as osteopathic, chiropractic, physical therapy, etc and get into the nitty-gritty of neurophysiology of counter-irritation, biomechanics of connective tissue, etc. DC's, DO's, PT's do very little meaningful research, but they try.
One interesting and emerging area is the analgesic properties of nitric oxide, arterial vasodilation, and physical modalities and exercise: Might this explain the "rule of the artery is supreme?"
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15289898&dopt=Abstract
Another interesting area is the cellular basis of protein synthesis, stretch, and physical strain: Might this help us understand the basis of myosfascial "compensatory patterns?"
http://www.jaoa.org/cgi/reprint/106/3/157.pdf
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16618703&query_hl=14&itool=pubmed_DocSum
Finally, some recent studies confirm that peripheral stimulation of nerves can modulate CNS circuits. This has *HUGE* implications for those of us in pain medicine, but also harkens way back to IM Korr and the "facilitated segment."
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16730124&query_hl=10&itool=pubmed_docsum
Science doesn't happen over night. It takes decades and sometimes hundreds of years to move from systematic observation to hypothesis testing. Medicine is complex. The MSK system is one of the most poorly understood systems in the human body. Locomotion is complex. Our understanding of pain is simplistic at best. So, you can see how jumping ahead to RCT's of manual medicine is frought is difficulties.
I have been where many of you are now. I sat in class rooms and OMM labs and listened to a lot of "osteopathic fairy tales." I did a lot of eye rolling too. Believe me, there are quacks and zealots in every part of medicine not just DO schools. Though it does seem that one unintended consequence of osteopathic schoools' selecting for "holistic minded" practitioners is a greater tolerance for the lunatic fringe...that's lamentable, but ultimately okay.
Still, the thing to appreciate about fairy tales is that while the details are invented or false, usually "the moral of the story" is true. For example, at my school we seemed to spend an inordinant amount of time addressing "the lymphatics." I remember as a medical students running around the ICU's at our community osteopathic hospital "balancing the membranes" and "treating the ribs" and doing all kinds of hokey-pokey things that certainly didn't harm, but I wasn't always convinced exactly "helped" either. This stimulated some students to really take the bull by the horns and try to address the mechanisms of these treatments in a rigorous way:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16314677&query_hl=18&itool=pubmed_docsum
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=11213665&query_hl=23&itool=pubmed_docsum
Ultimately, this is how the profession will answer these questions. Not by repeatedly beating each other up and bemoaning "the lack of evidence."