I know how you feel, I went through the exact same thing. I’ve got massive breasts, and they tend to draw you forward constantly.
Firstly, if you don’t have one already I’d recommend you invest in a supportive bra that fits you well, at least for your riding. That alone should increase your confidence, so maybe you can start riding around a little more ‘tits up’.
So the muscles that are tightening in your chest are called the pectoralis minor muscles. They look like this:
When you hunch over and pull your shoulders forward all the time these muscles become too tight. And if you’re like me and let it go on too long this can eventually cause back/shoulder pain that will have a massage therapist shaking her head at you over.
You can do your own trigger point massage to help loosen up your pecs, which helps some. The place I focus on are under the clavical where the pec meets your shoulder muscle, there’s an indentation there with no muscle. Use your opposite hand to vigorously massage that hollow. The other one I do is lift my arm to shoulder height, palm down, and with the other hand I grab the edge of the pec (it’s the front of your armpit, it’ll probably feel tendon-y when your arm is raised), and massage it forward.
Then lay down on your stomach with your head turned to the side, and slowly lift the arm that you’re facing straight up away from the floor a few times, then have someone hold it or prop it up for a few seconds and relax and breathe into the stretch. Then do it again with the same arm but with your head turned away.
Now stand up with your back and heels directly against a wall and slowly stretch out both arms up and then roll them down against the wall in a jumping jack/breast stroke motion. Feel how the shoulder blades draw your arms down and how your chest opens up. Don’t over do it, but this roll of the shoulders down feeling will come in handy later.
Once you’ve done all that your shoulders should be feeling really loose and heavy, and your chest should feel more open than you’re used to.
Okay now for what you’re experiencing. Anyone used to being in and around barns may notice that at my barn there is a notable absence of two phrases that you hear religiously from other instructors. The first is ‘Keep your heels down.” And the second is, “Push your shoulders back.”
My reasons are because almost without fail, “Shoulders back” creates that overarching in the spine that you describe. This is especially a problem with people who were born female, because our spines tend to have more curvature that way naturally.
When you overarch, your seatbones become displaced backwards and you tend to sit in a forked position. You want to be sitting on your seat bones and sort of suspended between your coccyx and pubic arch, so you have leeway to move back and forth with the motion of the horse. But the position that ‘shoulders back’ give you puts you too much forward onto your crotch, disengaging your seatbones and essentially taking the entire seat aid out of this picture.
I don’t feel that you can be a very effective rider if you ride without the seat.
So instead of shoulders back, try this sequence when you first get on and redo it periodically throughout your ride:
At the halt use the pommel to pull your seat towards the front of the saddle, then (or at the same time) bring your thighs away from the horses side and slide your knees back, you can do this one leg at a time if it’s easier. Relax your thighs down around the saddle and allow your ankle to relax so that your heel hangs in the stirrup. The stirrup keeps the toe up, I feel like this goes right over peoples heads when they say ‘put the heels down’. You don’t have to push the heels down, you just have to relax the ankle and let gravity do the rest of the work.
Now feel for the lowest rib in your ribcage. I want you to drop this towards the front of your pelvis - you will be slouching, it’s fine you’re supposed to at this point. This part is important because it fills up the arch of your lower back and takes the strain off those muscles. Suddenly ‘keep your back straight’ starts making more sense!
Now remember that shoulder roll against the wall you did earlier? Do that one again, and allow your heavy shoulders to go with gravity and drop, your elbows are anchors that draw them down.
Now pretend that there is a string tied to the top of your head and someone is pulling it straight up to the sky. Allow yourself to grow tall but leave the heavy shoulders behind.
How does that feel? If it’s done right you should notice a release of tension in your back muscles and your core will be engaged. Once you get used to this sequence of events they only take about a second to perform. You may find that when you’re properly aligned it feels as if you’re leaning backwards. If this is the case you’ll have to create new muscle memory by using that feeling as your baseline. If you have a friend or instructor tell you when it looks good it’ll go a long way towards helping develop your position.
As a final note, if the saddle doesn’t fit you or the horse you’re riding you’ll be struggling regardless of how much you adjust your position, so saddle fit is a really important aspect to consider.
I don’t have boobs but this is super good info for people who do so I’m reblogging it anyway!!