If you teach yourself to tense & un-tense these muscles in groups by practicing tensing and un-tensing them while watching TV, or while riding in a car (probably not driving, at least until you learn to do it) it will be easier to teach this to your horse. It can take some practice to tense & un-tense these muscles in groups. Keep in mind that “shutting a horse down” by the riding locking all 4 groups of muscles is a discipline, to be used when the horse refuses to listen or even take the rider’s commands seriously. Once the horse gets the hang of this technique, it should only be used when the horse is seriously ignoring the rider’s requests/commands. When you normally ride with very soft contact, the bit will be floating in the horses mouth, matching his forward momentum. When you tense & lock all 4 sets of muscles, the horse literally runs into the bit, and it will, at the least, be uncomfortable. It isn’t literally running the horse into a wall, but it can feel like that to the horse. When you start teaching this, you may have to calm the horse down after shutting him/her down, and then try again. It is also critical that the hand & elbow position not change. For this to work correctly, it has to be done solely by tensing & un-tensing muscles.