Tend to agree with Sparty and DOctorJay. From my own personal experience, I faced a similiar question going into residency. PM me for more direct information. The short of my decision was choosing between my top 3 programs, knowing I wanted to pursue sports medicine or pain, or both. I think prof moriarity point is well-taken that some sports fellowships like to look outside the box, but if they do not keep you after they tried you for 3 years, than maybe its best for you and them. You still will get great exposure to the sports staff, build relationships for future, and likely land in another great fellowship (saw this with our chief resident who matched to sports at another predominant PM&R sports program (not same institution trained at). There are few accredited PM&R sports spots and hopefully more in future. I think the fear of being "inbred" that Prof Morality might be hinting at is a common fear when programs consistently keep their own, but converse it true of programs that look outside their residents. You make your own path with help from above. best to position yourself in a place that points you down the right road.
IMHO being at a place where you will be exposed to sports on a regular basis is key. My number one program ended up not being in my home state or my spouses home state, but it was where I felt I would get the good overall PM&R training, excellent outpatient training, exposure to PM&R sports and pain, and fellowship opportunities in both disciplines. You need to remember you will need letters of rec from sports medicine physicians for sports fellowship whether you choose primary care or PM&R. Often, it is hard to get electives if there is not a well-established sports or MSK department in your residency institution. Also, if it is primary care based, they may favor FP residents or more conventional primary care based residents (ER, IM, PEDS).
Also, if you are interested in sports and spine stuff, you will want to be at a place that will allow you hands-on with fluoro and US procedures. If you are interested in primary care sports and team coverage, you will want to be at a place that will allow you opportunities to cover events, teams, and do some longitudinal sports care in clinic. Remember sports fellowships want to see commitment to sports, participation in team event coverage. letters of rec from sports docs, opportunities for sports research (abstracts, posters, papers, ect.), and procedures if you can get them.
IMHO, the top places to train if you are interested in sports from a PM&R background are Mayo, Harvard/Spaulding, Washington, Emory, NW/RIC, UC Davis, Stanford, Wash U St. Louis, Med College Wisc (mostly womens athlete focus). All these have good ACMGE accredited PM&R sports fellowships with various exposure to spine, EMG, and US per my sources and experiences as student and resident in two of their programs.Tthere are 12 accredited PM&R spots fellowships but these come to mind.
Utah has very good and reputable Sports and MSK fellowship shared with Primary Care Sports Fellowship. Typically they take one ED, one FP/IM and one PM&R resident each year, and often another from one of those specialities if funding allotted. Can do emg, i-spine, and US with very good collegiate and olympic sports coverage.
Colorado has a unique PM&R Pain Fellowship that functions like a sports and spine fellowship and has sports event and team coverage opportunities. However, you can only be boarded in Pain from here now that grandfather rules for Sports CAQ exam require you complete a 1 year ACGME accredited fellowship.
Other primary care programs that are good and take PM&R applicants are Iowa (no associated PM&R residency, JPS in Arlington, TX (multiple PM&R programs in Dallas), U of Florida (takes 1 pmr and 1 PC), Mayo Jacksonville, Indiana, Michigan (combined track that PM&R can apply to), Cleveland Clinic ( Metro Health has PM&R residency).
There are lots more. These are just some that come to mind.
Try to position yourself for where you will get good training, good exposure to right patients, mentors, and skills. Living where you want is good too, but you can usually always go home if you have right connections, build your CV, and work hard at the right place.