Keri performs a beginners substitution for the handstand push-up: knees on the bench and hands on the floor. The further the hands are from the bench the easier it is to do. As she gets stronger we'll move her hands closer in.
Sarah has progressed form doing her subbed HSPU's from the knees to a pike position on a plyo-box. Note how vertical her torso is. She is very close to performing HSPU's against a wall.