A recent study has demonstrated that, while ratings of perceived exertion (RPE) provide a simple, inexpensive, and valid method for measuring exercise intensity, measuring differential ratings of perceived exertion (e.g. RPE-Legs, RPE-Cardio, RPE-Technical) provides a more sensitive evaluation of the internal load.
Authors suggest that adding these subjective measures to the global session RPE can help coaches to better understand the true dose-response of team sports and better optimize subsequent recovery and training programs.
AthleteMonitoring.com can be used to efficiently capture and monitor differential RPE after each session. Example here: http://tiny.cc/r7we2x
Source: Weston, M., Siegler, J., Bahnert, A., McBrien, J: The Application of Differential Ratings of Perceived Exertion to Australian Footbal League Matches, Journal of Science and Medicine in Sport, 2004 (http://tees.openrepository.com/tees/bitstream/10149/336611/5/336611.pdf)