Light buoyancy...Play with it...
This ball is perfect for what I am using it for. Pinched nerve in my neck and left shoulder issue. Use this primarily for one arm kick/stroke drills. It has lighter buoyancy so my hand is actually in the water not above it, therefore I am in a more balanced position in the water. My neck and shoulders do not have any issues. (Kick boards made my neck and shoulders hurt no matter how we tried to use them. So boards are a no go zone.) Hand is in a natural position resting on the ball with light grip to keep hold of it. I have not used it under my chin, but on the "round side" of the ball it's not so easy to hold with my chin, but can hold the cupped sides with my chin (Breast stroke is not part of the program just yet). Have used it between the knees, different good not different bad. This ball seems very versatile just a matter of playing with it. Comfy little head rest/pillow when laying on the bleachers. :o)