It's a very individual thing too. If a 50 year old 50 pound overweight body, and long weekends, and 500 foot hills is all what you have to work with, well that's what it is. So you experiment and work with what you've got. So you develop your own science and medicine and set your own records, or whatever. I don't look down on the 300 pound hikers any more than I look down on the 150 pound ultra runners. They are both gods on some other astral plane in my books. I have to live in the 200 to 225 pound world, at least for now. Every age and weight class is a science within itself.