There's someone on this forum - I think the username is pedspm&R (see resident roster thread/sticky) who finished the U.Cincinnati peds/PM&R program. You might want to pm him/her.
The other research sounds interesting. I think at this point, the PDs will just be impressed you have research under your belt. However, if PM&R keeps getting more competitive, you may want to consider seeking out a Physiatrist to do research with. There's a MS2 at my school who already has publications in the PM&R journals and have worked with several excellent acadmic physiatrists. I think he is an exception at this point and he will have superb opportunities when it comes to residency.
Since you are an MS1 and you have the time and the option of choosing from various research projects, I really would try to find a physiatrist doing research. If you are not sure about PM&R and want to keep your options open, the peds research will keep you competitive for Peds, Psych, perhaps peds/neuro/dvlpmntl and Family Med. The Osteoporosis research will keep you competitive for endocrine/IM, Ortho, Family Med, and Geriatrics.
Looks like you asked the questions about Peds/PM&R already and I don't want to reiterate what you already know. I met a Peds/PM&R UCincinnati resident at the AAPMR conference - and she seemed very happy with her choice. I also met a Peds/PM&R doc who went to Jefferson. I'm not sure what her long term plans are - but she is working in Delaware as a pediatrician and working in Pennsylvania as a PM&R doc doing EMGs and pain management. (while waiting for her significant other to finish residency) I can try to get her info for you if you are interested.
Here's the link to U. Cincinnati's program:
http://www.med.uc.edu/pmr/content/overview_ped.cfm
Another link about Peds/PM&R combined programs:
http://www.abp.org/certinfo/genpeds/pmr.htm
The AAP link:
http://www.physiatry.org/education/pdfs/apx2part3CombProgs.html
I don't know where you go to medical school - so I don't know if there is a good PM&R department at your school. If there is, you can probably find some good research going on there. If not, maybe you can contact the nearest or most convenient residency program and find a project.
Even if you are not sure about your future, meeting as many physiatrists, finding good mentors, and learning more about your options will all benefit you in the months and years to come. Just being on this forum and asking questions also shows great motivation and you are way ahead of your classmates. Hope this helps.