The knee-chest position, also called genupectoral position, is a spanking position in which the spankee assumes the on-all-fours position and then lowers his/her head and chest so that his/her forehead touches the ground/mattress and his/her bottom sticks up into the air. This position is often taken on a bed.
The knee-chest position can be uncomfortable, e.g. if it puts too much pressure on the spankee's stomach. Spreading the knees slightly can help in this case. For male spankees, his spanker may dance lightly with a pendulous scrotum. For female spankees, there may be a desire to have the labia struck in a loving manner. Skillful spankers know to play to these needs.