Now I kind of want a system free book that takes several people (worlds strongest contestant, top level gymnast, top level decathalete, navy seal, parkour course star, and then a handful of less extreme cases spread out over the physical attribute spectrum down to couch potato, and gets them to do a bunch of things like climb, swim, break down doors, carry back packs, dig various holes, climb ropes with a backpack on, swim with a backpack on, see how long they can fast march, etc... just to have some benchmarks.