Wore it on just an overnight backpacking hike. No issues. Had close to 30 pounds, a little more than I should carry probably but we're just learning, and hiked up a mountain.

I did use mine with a 3500cu.in. (Gregory) pack at between 45-50 lbs. for 1 wk - bra was fine. ...had more problems with the waistband digging in at that weight...thought my collarbones did get a little sore at exactly bra-strap points but I get that with any bra.

I just wore mine under a 2000+/- cu. in. pack with about 20lbs in it on an approach hike (maybe 30 minutes?). I couldn't even tell I was wearing it. No strap issues at all. It was much more comfortable than any other bra I've ever worn under a pack. I can't speak to how it would feel with a 3500 cu. in. pack with 45 lbs in it on the AT or PCT for months, but I can tell you it was very comfortable as I wore it. Good luck and have fun!