Competitions - Arena shyness

I don't suppose anyone has had a horse that is too "arena-ised"? I broke in my first horse a couple of years ago. I obviously did too much work in the arena as he seems to be very sluggish in there now. I know he is a warmblood and they tend to be lazy (which he most definitely is) but he just doesn't like to work in the arena. Let me give you an example- I went to a dressage training day at Riverside a while back, and while I got him going forward BEAUTIFULLY in the warmup (I got excited thinking I might do a nice test) as soon as we got into the arena he backed right off, tried to discreetly move toward the other horses and I had a terrible time trying to get forward and look like it was all effortless!
Any ideas how to approach this one? My instructor has told me not to ride him in an arena at all if possible, so I haven't for about 5-6 months. He is more forward but again not in the competition arena. It is very frustrating!! Oh, and I am pretty sure I am still breathing during the test.....

well...if it were me i'd try two things
1. I'd try to make your horse actually like the arena. Try letting him loose in there, feeding him there, and just keeping it really pleasant. Also try riding in there in a more relaxed way so that he feels like he's on the trail.
and 2. make him like other places less. say if her hates the arena but loves i don't know...the paddock, ride him in there but get him to perform some difficult tasks there and give him a good workout. Don't do it so long that he comes to dislike the paddock, but long enough for him to be ridden other places as well.
i hope this works...

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I've found that while out at competitions, it isn't the 'arena' per se, it's more about leaving of the herd (in the warm up arena) and entering an empty space towards a car. And more than likely, as soon as the horse 'backs off' a tiny bit, the rider subconsciously begins to ride more defensively. So combined, the result is a horse which lacks the confidence to travel forward properly.

I've always taken advantage of competition venues which have lots of open space seperate to the designated warm up arena. That way you can warm up in both areas - near and far from other horses, mix up the scenery and really get the horse used to working in different environments. Eventually, trotting down the centre line of an arena is 'just another area' to work in, if that makes sense?

*edited* - Oops, just noticed this is a fairly old thread Embarassed