Depends entirely upon what, where and the details of how.
Edit: okay, found Paulick Report, which says
“We don’t do it a lot, but we shock-waved his back,” said O’Neill. “He gets a little tight in the lumbar area right behind where the saddle sits. It’s Paul Reddam’s horse, and he was OK spending the money to do the therapy.”
“This horse is treated like a king and he is a king,” said O’Neill. “We’re bringing a chiropractor to Kentucky. Shock-waving does help if you’ve got some tightness in the back, but it’s not the kind of treatment that is going to make a slow horse fast.”
So: exactly what is said above. It\'s just good sports therapy. Yes, they automatically go on the vet\'s list for 10 days, because some type of treatments can possibly decrease pain for a day or two.
Just watch him in the morning to make sure he doesn\'t have a sore back. Any track man will be able to see it at a trot and normal gallop around the track.