Engage your core!
How often have we all heard that? These vague instructions often lead riders to tense their midsection, leading to a tight back and a seat that can’t follow. This has the opposite effect as desired, and can create tense arms and hands, leading to further contact issues.
This does not mean you don’t want to use your core, however. But using your core is more about being in a position that allows for core engagement, with a neutral pelvis and soft lower back. This position allows for your core to do its job and to absorb and follow the horse’s motion.
I frequently find being in this position allows riders who were previously working their tails off to maintain a horse’s movement suddenly are able to breathe better and work less hard. This is because they can then allow the horse to do the work, and their bodies can follow and absorb motion instead of inhibit or block it.