What does three point contact mean when using stairs?

Three-point contact refers to moving on a surface and to how many of your limbs are reliably attached to a surface feature. For example, both hands on a rail and a foot on the step, or both feet on step(s) and a hand on the stairrail. Etc. In this case, three-point contact for stairs means holding both stairrails one with each hand and using one foot when stepping up/down the stairs. From a design point of view, the stair designer must design a handrail which is graspable (1-5/8" dia.) and a stair which is walkable preferably 7" riser and 11" tread. This will make three-point-control possible and achievable.