Sport boots or polo wraps are used to help protect and support the tendons/ligaments in the horses legs when used for strenuous activity.
They are completely personal preference.
Neither sport boots nor polo wraps will physically support the fetlock as much as the companies claim, but they do help a small amount. What they can be more beneficial for, is protecting the legs from hitting each other when making these speed moves.
Personally, for myself, I use Professional's Choice SMB 3 sport boots on all four legs, along with Professiona's Choice Ballistic Overreach boots on the front legs. I feel that boots offer more protection than polo's because I feel they are thicker.
Others will disagree with me and say that polos are better (this is why all this is a matter of personal preference and opinion). But we almost can always agree that you should NOT use polo wraps unless you know how to wrap them properly. If they are wrapped wrong, they can actually do serious damage to the tendons/ligaments. And they also could come undone duringn an event, and cause a big wreck.
It is important to remember that neither sport boots nor polo wraps should be left on the horse's legs for hours upon hours. These built up heat, and that can damage the legs. Always take them off in-between events to allow your horse's legs to cool.
Also, do not buy cheap sport boots or cheap polo wraps. Cheap is what cheap does. Stick with good quality name brands such as Professional's Choice, Classic Equine, Iconoclast, Pro Equine, etc etc. Yes, they are expensive but if you take care of the boots, they will last you for years and years.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.