It's far bigger an area than you probably imagined.
Your core covers everything from your sternum down to hips, including lower back, top of hamstrings, and glutes (peachy butts). Your pelvis is where you are meant to have the most stability in the body, so any muscle that connects to the pelvis is crucial to you having a stable core, and good balance. Think of your core as an anchor, its balanced and supported by the surrounding muscles. Mobility, flexibility balance and athleticism all derive from your pelvis. To improve your ability in the saddle and aid your horse better, you must take an integrated approach to core strength and work on several areas to improve overall.
Core strength is vital for riders to remain balanced and connected with the horse. It’s not the type of core strength that comes with doing 100 crunches each day. It’s the type of core strength that enables you to maintain a neutral spine with a balanced pelvis, creating the illusion of stillness when you’re riding.
To be able to ride well you must be able to use your strong core in movement patterns that are specific to the riding patterns. Training your core to stabilise your posture while you train specific rider movement patterns will teach you how to transfer your core strength to your riding.