"Are you plugged in?"
Deep in the saddle
Not until much later in my riding career did I start to realize that ALL of the rider's movement is connected. If there is not a strong foundation- starting with the seat- the rest of the rider's body will have unwanted "side effects" or excessive movement as a way to unintentionally compensate for a lack of balance and stability.
I won't cover my entire anatomical lecture, but I will discuss the starting point, where the foundation of a strong rider comes from- their seat.
First, do you know what your seat bones are? Whether you do or don't, let's experiment.
Find a hard, flat surface. Sit on it, with both feet flat on the ground. You'll notice you feel two pointy bones- one on the left and one on the right- pushing down into the hard surface. These are your seat bones. If you really want to feel them, place each hand, palm side up, under each seat bone. Then take your hands out, you'll really feel them now.
Now I want you to imagine an electrical cord, with the prongs sticking out. Think of plugging it into a wall outlet. If you only plug it in halfway, you will have inconsistent energy running through it and it will short out as a power source at times. If you plug it in at an angle, you may get some voltage, but soon it will tilt and perhaps even fall out of the electrical socket.
This is the same for your seat bones. If they are not what I call "plugged-in" to the saddle correctly, you wind up feeling like a sack of potatoes "going" for the ride. But if you are stable in your seat foundation, you then have the freedom to move other body parts without feeling like you will lose your balance.
The angle and rotation of your pelvis will affect the direction that your seat bones are when you are attempting to "plug-in."
If you overrotate your pelvis forward, your seat bones are pointing towards the horse's ears. This causes a curl in your spine, and you will "drop" your shoulders down towards your hips to unintentionally try to compress and feel balanced (think fetal position.)
Over rotating your pelvis toward's the horse's tail causes you to roll up onto your pubic bone, and to hollow in your lower back. This sensation causes you to always feel like you are falling forward towards the horse's neck.
So experiment with feel both "wrong" positions with your seat bones, and then stand up, re-seat yourself and find your center on the hard surface.
Then experiment with it in your saddle. Then start to notice when do you lose that "plugged-in" feeling- is it when you increase energy, make a turn, ask for a halt, etc.
Again, there is much more to my typical anatomical lecture and the trickle-down effect seat bones have on everything the rider does.
But if a majority of riders just started by raising their awareness as to where their seat bones were and if they were "plugged-in" at all times, many folks would feel far less unstable on the horse, and be able to increase their pro-active communication with the horse with improved timing because they wouldn't be distracted by attempting to "hang on" and feel balanced. The later causes riders to be reactive and defensive with their aids because of instability in the seat.