Runners stretch. They tell me (my running days are so far behind me that I can’t see them) that this is because the muscles used in running need to be loosened up to avoid cramping and pain. The biomechanics (skeleton, muscle, nerve, brain connection) of a horse are pretty similar to the human. After all, are we not both mammals? So when a human (you or me) chooses to ride a horse (Dobbin), it follows that some time must be spent in preparation by you and Dobbin. My old mentor had a more earthy way of putting it. He told me before I get on, warm him up in some circles both ways to “untrack him”. Then, after mounting, he said to warm him up in some more circles before starting out.
Generally when starting colts or retraining older horses, we do just that. We longe them, or ask them to walk trot and gallop around on a long rope both ways. The old Californios called these circles “las vueltas de muerte” or “turns of death”! That pretty well sums up the importance of warming up a horse! Then when we mount, we walk a lot. If we’re doing arena work I try to circle the arena both ways at the walk with reins as soft as possible. I don’t give any more direction than necessary. And mostly leave Dobbin alone. I don’t care if he goes straight or not, just so he moves and get his nerves and muscles and bones “oiled up“. Then we move on up to trot, and more direction from my aids (seat bones, legs, and reins). If we’re going outside I will walk him a good piece then trot a while on a soft rein before asking much. If he’s got any kinks in his back, or if it’s a fresh morning, or a windy day, this time will allow him to get a little more relaxed and “with me“.