DoubleScrubBrush

This man in the shower is using a standard one headed backbrush notice how this brush comes down to a certain point on the back DoubleScrubBrush can reach a greater area than this brush can

one headed backbrushes such as this curved backbrush can only reach a limited area of the back

another one headed backbrush with another backscrubber 

this man is using the one headed backbrush with DoubleScrubbrush  he can reach a greater area of the back

This woman is using a scrubbing pad to wash her back notice she has a very limited reach DoubleScrubBrush can reach more of the back with one stroke compared to this scrubbing pad

This woman is using a backscrubber it also reaches a limited area of the back