>General Running>Running between easy and hard efforts
What I hear from "back in the day" was that folks in the 80s ran medium efforts quite often -- and had much faster general races as a result.
Of course this only works if you are somewhat fit to begin with. If you are overweight and sit in a chair all day, then to avoid injury you will probably have to run very cautiously and very easy. But it's not the running at medium paces that is causing the injury then, is it.
The Logic of Long Distance