Rotational movements need the most thoracic mobility. This is because a rotational movement (such as twisting) because the movements are more three dimensional, and this is where the most can go wrong. For example, if you were holding a 35lb child and simply bent forward to put him/her down, this is less likely to cause injury than if you were to twist your torso to the right and put the child down. There is a lot more spinal stability and mobility needed for the second motion than the first.