I guess I'm lucky in that, for the most part, I run into fatigue before I run into pain. If I overdo things, my left knee (the one that had to be almost completely reconstructed 23 years ago) starts aching. Most of the time, though, the knee is OK unless my pack is too heavy or I've tried to hike too fast on extra-long downhill stretches. It has become obvious that I had better not plan on longer than 5-7 mile days (less if off-trail). If I try to do more, I can end up hurting all over by the end of the day, especially if there's a lot of downhill. I try to keep my trips easy enough and my load light enough to avoid pain. I'm out there to have fun, and when I start hurting, I'm not having fun!

I don't have particular discomfort from my pack as long as I keep the load lifters tight enough to keep the shoulder straps from putting any pressure on my shoulders and to transfer basically all the weight to my hip belt. I really lucked out with my pack (2005 model Six Moon Designs Comet). I assumed, after ditching my old external frame Kelty and not finding anything I remotely liked at REI, that I'd have to order and return at least half a dozen packs before finding what I wanted. The SMD Comet was the first pack I ordered. To my surprise, the pack felt as though it had been made to order just for me! I suspect that those having pain from their packs might either need a better-fitting pack or are trying to carry too much weight, or both.

Since switching from boots to trail runners, I rarely have foot pain unless I'm carrying too heavy a pack. This is weird because I have really deformed feet (bunions, hammertoes, fallen arches). Maybe I have a high pain threshold (though that's not evident when I visit the dentist!). I do need shoes with good arch support and anti-pronation features--none of those "barefoot" styles for me. Body Glide on my feet helps, too.

The real pain for me comes at the end of the day, while sitting around camp or, especially, lying down at night with the resulting pressure on my hip and shoulder joints. The summer I tried to convince myself that I was comfortable on a NeoAir was particularly awful. I was constantly tossing and turning trying to get comfortable and usually rolling off the stupid thing as a result. The weight savings definitely were not worth the considerable loss of comfort.

What has served me well, so far--all learned the hard way, BTW:
(1) Cut back more and more on pack weight as I get older.
(2) Find more comfortable gear (if necessary, cutting weight elsewhere) to fit my particular needs.
(3) Plan more flexible trips with shorter days and more layover/contingency days so I can tailor my trips to how I feel at the time (that varies, too!). I suspect that in the future I'll have to cut trip length so I'm not carrying so much food at a time. For example, I have a 10-day trip planned this summer, but it's one I can cut short if needed. At least I'll know the first day if the weight is too much for me, so I can stop and do some dayhiking, using two of the three planned layover days while I eat up some of the food!