Backpacks with concave curve - more comfortable?

I feel strongly that weight training has helped me with being able to handle the rigours of backpacking. The one exercise I do to help with putting on the backpack is with using a weighted ball. I place the ball on the ground, with my feet spread a bit, next to my foot. I pick the ball up with both hands amd as I straighten up (stand) raise the ball over to the opposite shoulder. I do 3 sets of 10 reps with increasing weight for each set. Good luck.

Yes. But perhaps not how you think.

We use framed packs with hip belts so that, ideally, our torso (shoulders, spine, back muscles) carries none of the pack's weight. The weight travels down the frame, into the hip belt, and right onto our hips (then legs, feet, and finally ground). Why shoulder straps then? Mainly for leverage; if not for the should straps the pack would flop backwards and hit you in the backs of the legs because the pack's center of gravity (CoG) is not directly above the pack/hip-belt connection.

Knowing this structure, consider now the concave arch touching your body at only the shoulder and hips. The shoulder point used for leverage -- check -- and the hips point for transferring the weight -- check. However, unlike pack-framing formed to the spine's curvature, the arch will tend to hold your pack's CoG further away from the pack/hip-belt connection (and further from your own, resulting in slight adjustments to balance), if only by half an inch. This will result in a wee bit more leverage pulling backward against your upper body.

On the whole, you'll notice that the muscle group resisting the pulling back of those shoulder straps is your core muscles.

With respect to your situation, I agree with Tigger. The pack that best fits your unique shape will be the most comfortable one you can use.

For touring travel (as compared to the wilderness self-contained backcountry camping on the ground out in the open travel that this site is mostly about) I'd lean more towards a wheeled smaller duffle perhaps than a backpack, something carry on compliant would also make life simpler. And frames get damaged when on and off too many transport baggage compartments....

www.timbuk2.com/copilot-carry-on-luggage-roller/544.html

Just keep the burden off your back entirely. maybe with a supplemental bike messenger bag for things you never want off your body? I like the top loading access messenger bags provide especially in cities where I NEVER want to have to put my important possessions down as I would to get at them in an actual backpack.