I consider this course (or any similar one ) a basic, which should be audit by anyone interested in the bioengineering systems.
http://ocw.mit.edu/OcwWeb/Biological-Engineering/20-430JFall-2004/CourseHome/index.htm
unfortunately many of the lecture noted offered at aboive address are very hard to understand , but the outlines will point to many interesting directions of self study.
Ill try to find some EMS devices info for you on net, I own some books of medical electronics (EEG, EKG , EMS and other devices )where I got the basics , but they are in my native language. Im 100% positive medical electronics books are widely available in your country as well.