Complex sentence: Dufnering is a variation of planking that involves a person laying with the bottom half of their body on the floor, the top half leaning up, their arms close to the side of their body, and their hands ending towards the bottom of their thighs.
Split into simpler sentences: Dufnering is a variation of planking where one would lie with the bottom half of their body on the floor and with the top half leaning up. One would put their arms close to their side with their hands ending towards the bottom of their thighs.