the "weighted pack" plan is all well and good IF the training individual has been doing that already - you start someone off walking inclines, hills, stairs at 55 or older that isn't used to that and you'll have injuries nearly for sure and they won't be easy to recover from - I am 68 y/o, been doing all sorts of weight (heavy weight) training and stairs, lots and lots of stairs since my 20's - I'm 18 mos. post bilateral total knees, two rotator cuff tears (complete tears), treated hypertension since early 30's, osteo inflammation cycles present for who knows how long, - IF you want longevity you'd better 1) get a good orthopedic surgeon to consult when needed 2) KNOW your body AND system 3) get AT LEAST 8 hours of sleep (good sleep) every night 4) learn to let yourself rest & recover when it's needed - I overtrained for YEARS, had quite a few trainers that were good friends but I refused to acknowledge that they knew more than me, backed off and paid closer attention and NOW, I won't be the first to the top of the canyon with an elk hind quarter in the meat pack but I'll certainly get there and be able to repeat the next day (and as needed) LISTEN TO YOUR BODY, nobody's the same …..