I think you have got a misconception of the whole bar system. Using a bar as a control system wont save your arms from getting sore on its own.
You need to use a harness to remove the strain from you're hands. The strop (or line) between your handles is used to hook round a roller on a harness, or if you are using a bar then you would hook the loop in the middle of the bar around either a roller if thats what you have or the hook on you're harness. Then the pull from the kite would act through the harness and onto you're lower back and hip/bum area.
This means you can fly with one hand or let go of the handles / bar completely.
Most people who have flown kites for a while use a harness either with a bar or handles and there are a few systems out there which I will list below. If anyone else feels I have missed anything important then do feel free to correct me

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Handles With Open Roller:
Best starting system with handles. Peter Lynn Kiting harneses come with a roller which is open at the bottom, so you hook your strop up onto it, and as long as the kite is pulling the line will stay on the roller, but you can take it off by pulling back and letting the strop fall loose and away from the roller. Best way to start as you get used to the idea that letting the kite go doesnt mean u'r free from its pull - especially when it goes wrong!
Hook With Bar:
Good if you intend on using a bar. Most kitesurfing harnesses come with a metal hook which the 'loop' on the bar connects onto. Most bar systems have a quick release system on this loop which allows you to either kill the kite or ditch it totally if something goes wrong. And as such are pretty safe.
Closed Loop Roller:
Generally used by Buggy Racers, Freestylers and more experienced kiters. This is usually a custom set up, consisting of a sailing style snap or swivel block. And a wichard quick release. The idea is the same as the roller system with the difference that you cannot simply unhook the strop. Its closed into the roller. This is where the wichard is crucial, it allows you to get rid of the block, handles and consequently kite by pulling the quick release. I personally prefer this set up as you make it to suit yourself and can work it better. Plus bars, handles, everything else can hook into it.
I'm sure others will have photos online demonstrating everything i've spoken about and there will be more to say and add onto this. But think that covers the main points and has to be one of my longest posts in a while, so sorry if anyone has fallen asleep

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