A while back I wrote a post about finding your "lean body" weight and then finding how much fat you carry. Take a percentage of the lean body weight as your maximum comfortable load and then subtract your body fat from it and you have a realistic number. The 1/4 "LORE" refers to "fit" people. Obviously my fat 240 pound friend who has lots of muscles, cannot carry the same % of his body weight that I can.

So I am 175 pounds and 10% body fat, or 17.5 pounds of fat, and I take 1/4 of my lean body mass ( .25 x (175 - 17.5)) we arrive at 157.5 pounds lean body mass. .25 x 157.5 lbs = 39.4 pounds (max theoretical load). If I then subtract 17.5 (my body fat) from 39.4 -17.5 = 21.9. I think that's a tad low, however lets face it, today's hikers are wimps and the low numbers are in line with everybody complaining about carrying the packs that we considered normal in the good old days.

When I was younger and maybe still 10% body fat and weighed 145, the calculation would say that should carry an 18.5 pound pack, yet I was very comfortable with a 32 pound pack.

Unless you are very fit you probably have 18% to 33 % body fat. If you weigh 200 pounds and have 25 % body fat, then you are carrying 50 pounds of fat. 25 % of your lean body mass would be 150 x .25 = 37 pounds. If you subtract 50 pounds from 37 pounds you get a negative number, which means you will not be comfortable going up that trail with anything on your back.

I think the equation should be done by actual body muscle mass but that is very difficult to measure, however hese numbers do indicate WHY modern bpers need UL packs, they're not physically fit by old standards.
Jim