Sally Swift in her book "Centered Riding" was ahead of her time! An amazing exercise that Sally speaks of in her book will change your riding ability and if the spine with its associated muscles function normally you can achieve full uninterrupted turns.
Sally has you hold your arms at the horizontal and twist at the waist while keeping your arms horizontal. The second phase is bring the arms down like holding a ball and twist again. Finally she has you bring the elbow in and repeat. She makes note of the fact that you may have some restrictions both right or left. In terms of your movement if your spine has subluxations within the thoracic or lumbar you will not turn equally. Chiropractic adjustments along with exercises will enhance your riding without a doubt as well as your horse's ability to move freely.