Sentence:  Place a suitably loaded barbell across them ; grasp the bar ( which will rest against the back of your neck ) ; extend your feet forward and backward until you are in a <WSD>deep</WSD> leg split . 
Meaning of the word marked with <WSD> tags:  having great spatial extension or penetration downward or inward from an outer surface or backward or laterally or outward from a center; sometimes used in combination