Every harness has a cummerbund, right?

The cummerbund is easy to do up, and holds the harness in place while you connect and tighten any clips or straps or buckles to the bar.

Does the cummerbund have any other purpose?

Don't think so. I don't even use mine on my mystic shadow. It is still tucked away like when I first bought it.

Might add some protection for those who don't wear a rash guard or don't use a bar pad.

Yes!
This is what it does to men (keeps your guts tight):





And this is what it does to women (acting as a push-up bra):





Sorry to both of you but I could not resist...

Cheers
Caesar

That's my friend Hege here in Cabarete! LOL

The cummerbund makes for a smooth surface over your stomach so the harness is in contact all the way round. I am guessing your gut could get caught between the edge of the harness and the bar pad without it.

My Cabrinha harnesses have a pair of elastic "power belts" that stretch over the cummerbund. In support terms they don't do anything useful but they do cover the hook velcro on the cummerbund and stop it eating out the back of the bar pad.

A cummerbund is designed to increase intra-abdominal pressure, which stabilizes your entire midsection I think. A bit like a weightlifting belt.

Weightlifting belts are bad for you unless you are actually competing. When lifting weights you want your abs to develop too! The belt tends to weaken your abs because it allows the belt to take much of the load. Lifting without a belt develops great abs.

All I know about cummerbunds is that some of those old harnesses would poke the hell out of you the spreader bar would jab you in the ribs and the cummberbund was your only chance at not gettting speared.

today the harnesses are so much more comfortable so cummerbunds are about as useful as spats and monogrammed handkerchiefs

As a physical therapist I am well aware of the consequences and risks of using a weightlifting belt. It's good to hear that the myths about these are dissapearing.

I do still think there is a good reason why kitesurfing harnesses have them though.. The forces projected on your spine while jumping, doing kiteloops etc shouldn't underestimated and are on another level then those while casually lifting weights.

(its hard for me to explain the difference of force because of the language barrier)

A harness does not and will never act as a weight lifting belt. Don't ever think of it as one because it is not. If you have ever worn one properly you would know just how tight and uncomfortable they are. You would most likely not even be able to make it to the water without passing out from lack of oxygen.

just kite without a cummerbund you'll see. On a modern harness makes no difference. On a harness from 2003 it will poke your ribs so hard you won't be able to move for days. It's a relic.