I would like to impress upon people the importance of simply Warming up your horse for any type of work. I don't care what discipline you ride you need to warm your horse up in what ever way seems appropriate to the individual.
I tend to address training often using simple logic and this is one of those areas. If you are working your horse at a certain level that requires any suppleness, strength, cardio, or athletic difficulty, you need to warm your horse up properly.
Some things that I will do is read my horses posture to know if my horse is ready to start more demanding work. The video shows what posture I like to have in my horse before I start to ask them to do more focused work.
Ask yourself if you went to work out or do a Yoga class, would you want to go right to a bunch of really difficult exercises cold or would you like to loosen up first and gradually get into more challenging things little by little.
Another thing to think about is how we often try to cram a horse into outlines or frames they would actually choose to take naturally if they were given a choice and a bit of time to relax into it. With no help from you. Yes, The horse would actually offer the very thing you were trying to make happen manually and too early in the ride. This could also cause undo strain and injury to a body that isn't ready to go there yet.
When it comes to arthritic and older horses it is even more important to take longer more gentle warm ups to make sure joints get plenty or blood flow to increase mobility and flexibility. These horses will stay sounder longer and work happier and more comfortably.
I have lots of things I do and they vary from horse to horse from hand walking for several minutes to mounted exercises. I have several video exercises some are more involved then others. Some are on the ground and others are mounted see below for examples.