It's a competitive world out there. Unfortunately, there are people who make unethical choices to gain unfair advantages in their show ring pursuit of that championship ribbon or trophy. Even more unfortunate is the suffering that these choices cause to the horses.
When someone deliberately causes pain to artificially exaggerate the leg motion of a horse's gait, it's called soring. The practice is commonly used on "big lick" Tennessee Walking Horses, but other gaited horses may also suffer from this practice.
Regardless of whether soring is done using chemicals or physical methods, it's unethical and illegal. It has always been unethical, and it's been illegal since 1970...but it continues.
Want to learn more about soring and how to stop it? There are many resources to help: