In a spinal rotation around the axis of the spine (without side bending, flexing, or extending), note that the muscles that are concentrically contracting on one side of the body are eccentrically contracting on the opposite side. This ends up meaning that one layer of abdominals is concentrically contracting while the layer above or below is eccentrically contracting. This layering allows for a very finely tuned modulation of spinal actions and balance in the whole circumference of the torso.
Binding the arms in any position has a strong effect on the shoulder girdle and the spine. The anterior–inferior part of the glenohumeral joint capsule is the most vulnerable to dislocation. The binding of the arms in internal rotation and extension puts pressure on this part of the joint capsule, especially if the rest of the shoulder girdle is limited in its mobility. (This caution applies to binding in general because it allows for more leverage or force to be directed into the joint.)
In the process of coming into the bind, both the scapulae and arms abduct and then adduct. The adduction of the scapulae is usually the final step. If the scapulae have been depressed (pulled down the back) in addition to their other joint actions, their mobility is compromised.
Another compensation that happens if the shoulder girdle is restricted is spinal flexion. Flexion of the spine combined with rotation of the spine leaves the joints of the spine vulnerable to overmobilization. It is possible to use the leverage of the arms in their binding and against the leg to force the spine past an appropriate range of motion.