Soring has a few different names. It can be called fixing, heating, and doctoring. It is a, some say "training", technique that is done to give a padded Walking Horse a bigger, more animated gait. In my opinion, it is a shortcut to try and get to the winner's circle. Trainer's nowadays are too lazy to actually train a horse, so they take the easy way out. Easy for them, not the horse. If a padded horse is ridden soundly, not sored, they most likely won't win because there will be a trainer or two that slips past inspection with a sore horse and takes the glory from the trainer who should actually win.
Now, the actual practice of soring can be very gruesome. There are many different ways that trainers sore their horses. The most common practice is applying caustic chemicals such as mustard oil, gasoline, kerosene, diesel fuel, etc. to the pastern area on the front legs. Or, for a less chance of getting caught, some trainers put foreign objects(screws,nuts,golf balls, etc.) on the frog of the hoof before the farrier puts on the pads. Or they have the farrier trim the hoof too short so it is more sensitive. The pain when they set their front foot down makes them shift their weight to the back and that causes them to lift their feet higher.
If chemicals were applied to the leg then the horse's front legs are then wrapped in paper towels, then plastic wrap, then quilts, and then a leg wrap so they can "cook". Now, just because a horse's leg is wrapped, it doesn't mean the horse is sore. Honest trainers wrap their horse's legs to prevent the horses from injuring themselves, or to hold on medicine if a horse has injured itself, or some trainers put lotion(animal-safe) on the horse's legs to keep them soft so that they don't get as tense between riding sessions.
When it comes time for the horse to be ridden again, or shown, the trainer's take the wraps off the sore horses and sometimes apply a topical anesthetic to numb the area to pass inspection. Some trainers paint the leg hairs black and rub saw dust on the feet to give them a more natural feel.
There are ways to tell if a horse is sore, which is what DQP's (Designated Qualified Person's) look for when a horse goes through inspection. The horse may have wavy hair growth on the front legs, be unwilling of having his feet handled, have scars(which is not always as accurate), fall down when his foot is picked up, try to run away, have discharge or sores, and unnatural texture of the skin and hair.
Soring puts a bad light on our Industry. Not as many people sore as is believed but it is difficult to convince people of that. I hope to bring to light the fact that there are honest trainers out there still. I also try my best to help bring people that sore their horse's to justice.
You may wonder how I know so much about soring. When I was ten, before I knew what soring was and was so opposed to it, I rode with a few people that sored their horses. Everyday I saw the chemicals applied to their horses. I am ashamed to think how stupid I was and how I should have realized what was going on, but when I found out what it was, I never went back to the barn again. Now I work with honest trainers and I am proud to say that I show Sound Tennessee Walking Horses.
That is just a very brief description of soring. If you would like to learn more there have been many articles written about it that you can research on the internet. Also, a trainer who previously sored his horses(no longer), published a book about two horses that he sored, and it is written in the horse's point of view. The book is called From The Horse's Mouth by Eugine Davis. Eugine Davis is a pen name.