It's time for a change of topic, and I am going to go for breathing. Breathing whilst bearing down is a cornerstone of riding skills, and hard for almost everyone. Take a few breaths and notice, do your ribs lift at the front? If they do, and if an in-breath makes you taller, you are breathing into your upper chest. This is not a great breathing strategy for life as well as riding. It means that you are likely to be a hollow backed, both on and off horse. Your attempts to fix this will be frustrating, because every inbreath lifts you into that posture.
When you inflate the lower part of the lungs you have a much more efficient breathing strategy, which goes with a much more viable posture. Your lower ribs are allowed to expand outwards, making a bigger diameter and a bigger circumference to the 'circle' of the rib cage, but they are not allowed to lift up.
Anatomically, your diaphragm is like the cap of a mushroom, with its edges connected to your lower ribs. It keeps your lungs separate from your guts, and on an inbreath it is pulled down, making room for the lungs to expand into.
Imagine that someone has bought a big pile of loose shavings, covered them with a big tarpaulin, and put tyres on the edges to hold it down. If the wind gets in under the tarp it billows up. This is like upper chest breathing. Imagine deep sobbing, which is the extreme of this strategy. In diaphragmatic breathing, it is as if there is a suction pump at the bottom of the pile of shavings that sucks the tarp down on the inbreath. This will make your lower ribs expand but not lift.
So imagine this within your body, and maybe put your hands around your ribs, feeling them expand without lifting, and think of the suction happening from low down in your abdomen.
At first, this can feel difficult and stressful, and after a few breaths you will probably be longing to gasp, and lift your ribs. Do this if you must, but come back to the new pattern. Practice whilst driving your car - for you need to master this way of breathing, making it how you breathe all the time, not just when you are riding. I guarantee that you will not breathe one way 23 hours a day, and get on your horse for hour 24 and breathe differently.
In time, breathing 'down' rather than 'up' will leave you taking deeper, slower breaths, and you will supply much more oxygen to your muscles. This will increase your endurance, and perhaps even lengthen your life! It will certainly improve your riding, and it will encourage your horse to breathe too, for he may well take his cue from you. Like people, some horses are naturally much better 'breathers' than others, and good work can change their breathing pattern. When the horse begins to breathe diaphragmatically he usually begins to snort, and this is a sign that his body is releasing in a really good way.