No matter which category a horse falls into — hot-blooded or cold-blooded — riding him outside the confines of an arena and taking him down the trail is one of the best things you can do for him.
Riding outside gives cold-blooded horses a reason to go somewhere. They’re already unambitious as it is, so when you close them in an arena with four walls and they’re forced to see the same four walls every day, it de-motivates them even more. But when you get them outside and actually give them a place to go, it motivates them and adds a little spark to their step.
Riding outside is also good for horses that tend to be grouchy or sour because it keeps things interesting for them. The worst thing you can do with these types of horses is drill on the same exercises in the same boring arena every single day. By taking them outside, you can keep practicing the same exercises and train on them as much as you want, and because the environment is new and interesting, they don’t seem to get sour about it.
Training on the trail is also good for hot, nervous horses because it gets them exposed to all sorts of different objects, situations and environments. The more they’re exposed to, and eventually get comfortable with, the more their comfort zone expands.