I recently brought home from the library 52 Ways to Walk by Annabel Streets (yes, I believe that is a pseudonym). Didn't know what to expect, but I find each short chapter has interesting tidbits about ways to get the most benefit from a walk, whether taking a short (twelve minutes for best benefit) walk to break up a sedentary day, or taking an hour long brisk walk, or a slow stroll....
Lots of references in detailed Notes at the end.
Highly recommend.