I did a general rotation (4wks of spending days doing TBI, P&O, EMG, Ortho, Wheelchair, Nursing Home, pain, and acupuncture) and then a specific rotation (2wks TBI, 2wks SCI). I think the general one gave me a great overview of the field - and I was able to have a good interview with any interviewer in PM&R because of my exposure to almost all the aspects of PM&R. The specific ones helped - because it allowed me to get to know attendings well enough to get LORs out of them. If you know that a program is strong in a sub-field, it may be worth it to do a 2wk elective in that aspect - but also try to balance it out by rotating through other sub-fields. If you already have a specific interest, it may be of value to pursue an elective in that and perhaps do some research related to that interest. I think though, that many PDs look for compatibility of the applicant with the field and the more broad an exposure you have, the better you look.
If you only had exposure/experience in one sub-field, say, Sports, how would the PD know if you can function as an effective resident during in-patient rehab rotations? Many of the residents who were unhappy/burnt out at their programs found out during their residency that they hated a certain aspect of the field. God forbid, it's one of the longer required rotations (ACGME), you're going to be one unhappy resident for those months. I think by showing them an understanding of what you are getting yourself into, you are showing a level of maturity and sophistication instead of a superficial desire to go into an easy-lifestyle field.
