what’s the elastic chest strap for between the shoulder straps

"The sternum strap is great for people with non-trivial pectorals"
Wow – never heard boobs called non-trivial before!!! :-) (Br3sts are profanity, but you can call them boobs??? really?!)

For most women they are a necessary evil…. but there is a very narrow margin for positioning the strap between creating excessive 'trail cleavage' and choking you! A lot of pack designers don't get this 'small' detail correct, but most guys don't complain either! ;-)

Need for the strap really depends on the cut/design of the shoulder straps and their subsequent fit to the wearer.

I've recently been messing with the shoulder straps a lot more during a hike. By this I mean loosening a lot, or tightening up and clipping the sternum strap, or loosening one side, then swapping which side is tight, or hanging the pack off first one shoulder then the other student-style.

This works wonders for fatigue and irritation. It also allows me to air out my back for a while. I could never have done this in the old days with 40+ pounds to swing around.

I'd like to be able to swing the whole thing around front for a while too – perhaps to make up some snacks or retrieve a bug net for example. I can't figure out a good way to rig such a facility.

Not sure why I'm so averse to just stopping, but I find I put off things until I reach some imagined goal before I do and then it is overdue. Sunscreen or DEET are good examples. And I really dislike batman belts.