Using your Core
Your core muscles are really important when riding (as are your horse’s!). If you don’t use them then you will struggle with your balance and control and you will possibly get a sore back as well from slouching in the saddle.
When you engage your core, your body becomes much more stable and you have more control over your body and your horse. Your rising trot, sitting trot and jumping will all improve if you have your core engaged. You should also find that after a while of concentrated effort to engage your core, it will happen automatically and you won’t feel it hurting as you use the muscles!
Your core muscles will help your upper body remain tall and will improve your position and seat. There are lots of unmounted exercises you can do to improve the strength of your core muscles which will really help your fitness to ride your horse improve.
It may feel like a slog to begin with, but it will really pay off.