I'm working with an ex racehorse who like most, doesn't engage his hind quarters, round his back, or back up. Since my main discipline is barrel racing, I was told by a trainer out here to try a German Martingale on him. It will keep him on the calm side while he learns the pattern, and it helps him balance himself? What are the downfalls and pick ups of using a German Martingale on a horse? What all would it help with?
If you can't engage his hind quarters or collect him (round his back) then you have ZERO business teaching him the barrel pattern at this point in time. And doesn't back up??? That's an absolute basic fundamental.
I understand he's an ex-race horse and doesn't know these things. Yes, he needs to be taught. But he needs to be taught these things BEFORE you start him on barrels. And I don't care if you are even just walking it. You can't place his body into the proper position if you can't control every piece of his body.
A German Martingale can be a useful tool. The problem is that most people only get results with the GM and then when they take it off, they're back to where they started. Yes, you'll see some barrel racers actually run the pattern with a GM, but I personally think that's just laziness for not taking the time to train your horse, and relying on the GM.
Bend, bend, bend, and more bend and tons of circles will help your horse with collection and engage that hind end. And time. This ex-racehorse has been allowed to live the first part of his life with zero collection. It's going to take time to develop the muscles for him to carry himself in such a frame.
Elevate that inside rein, and use your inside leg to ask him to bend around it. Doing circles is going to teach him to bring that outside leg underneath him, and engage the hind end. Which is going to help him to collect, which is going to help him travel better.
I have used a GM from time to time, so they're not always bad. But softening your horse in the bridle and doing lots of bending and circles will be what actually teaches your horse to travel in a collected and relaxed frame, with their butt underneath them. The GM only works on the face/neck, and we need to work on the whole body.