Sitting on a horse turning in a circle; a large circle or a volte (10-8 meter circle) but a circle nonetheless, no straight lines. The center of a rider needs to stay balance on the horse as the pair is turning. For the horse to remain balanced through the turning, a rider’s core and seat must engage in the correct position.
The Abdominal and Oblique muscles with the Latissimus Dorsi engaged for the rider to stay in the position for turning or circling a horse. Lower back muscles stay supporting the seat but are not activated to signal rotating in the core. Most riders can move freely in one direction and not in the other. Turning one way is usually easier than the other direction. This is a sign that one side of the obliques are restricted or undeveloped.
I could go into more details as to why the fundamental of turning a horse correctly with the seat is crucial for riding. But for now, digest which muscles can help get the seat balanced while rotating the core centered in the saddle.
Outlined are the three major muscle groups responsible for the rider to rotate through the core. The video below gives my favorite, quick group of exercises; using one machine or just a resistance band! This would be considered one group for the workout. When muscles are conditioned for this job on a horse, which again is a fundamental for turning a horse in an area. The degree of core rotation depends on the size of the circle or turn.