this is not for guitars especailly
but could be i suppose. I have seen
a vest-like harness which some folks
have adapted for use with th nyckelharpa.
it has cross-pieces which go over each shoulder
to distribute the weight . The nyckelharpa
strap usually goes behind the neck and
over both shoulders and i have found at times
the weight of the instrument causes tingling
in the neck and fingers . apparently others
have experienced this too, and have invented
a thing that resembles on of those velcro
lumbar support belts that protect your back
if you are doing heavy lifting. i cannot find
a picture right now, but it is an interesting
way to support and distribute weight. will look
for a foto to describe this..