Science of Exercise

I'm looking for some in-depth information on what I guess I would coin the science of exercise. More specifically, i'm looking for information regarding the changes an individuals body goes through when reducing run times, improving strength, ect so I can train these attributes in a manner that is most effective and efficient. I have researched quite a bit but have not found what I was looking for. I'm sure many of the members of this board can point me in the rite direction: book, website, or whatever other source of information. Any suggestions would be greatly appreciated!