Comparable parts is a concept found in Sally Swift's Centered Riding. The idea behind comparable parts is that what we do in a specific area of our body directly affects that comparable (equivalent) body part of the horse. One time during a Centered Riding lesson I focused on relaxing my tongue without being told to do so. My instructor was watching the horse and not me. "What did you just do? He just relaxed his mouth!" she said, and this is when I truly learned the power of comparable parts.
Self-carriage is a term you will hear often in horsemanship, and it can be defined in many ways by many different people and disciplines. Commonly it is defined by the horse having a rounded back and engaged hind-end with the weight being shifted toward the hind-end causing lightness in the forehand.
Okay.... So how does this all come together?
Before she introduced this concept to me, I had created a physical cue for myself to trigger my PSNS. This goes back to a weight-loss method that involved touching finger to thumb on one hand to correlate with endorphins during exercise. My trigger was to pull my shoulders "back" ("back" can cause you to hollow your back, so I think shoulder blades together and reach my shoulder blades toward my hips). To establish this trigger I needed to mentally condition an endorphin release with the physical action. As I pulled my shoulders "back" I would imagine myself at ultimate comfort relaxing on a beach getting a massage. Now I have a trigger to relaxation that also helps my posture!
Now on to riding! I ride a very sensitive and forward TWH. Often times I get anxious riding, and especially if he is in "dragon mode". Now while I am riding I check in with myself and go over the techniques above. By doing this I have absolutely felt the benefit in myself. BUT the benefit doesn't stop there! I quickly realized my horse was moving better, but not just because I was less anxious. I've ridden him calmly and confidently and he still hadn't moved this well before.
I noticed he was improving in self-carriage. When I pulled my navel to my spine I was engaging my core and this was helping him engage his core. Rotating my pelvis under helped him rotate his pelvis under and to engage his hind-end and reach more underneath himself. Pulling my shoulders "back" instead of letting them collapse freed him to also lift his shoulder and round his back.
By activating our PSNS as riders, in addition to encouraging relaxation, we are improving our own riding and causing our horse to improve in self-carriage through the power of comparable parts.