I just remembered another one, I've added to my routine!

Get into a pushup position with your knees on the ground and your toes/feet stuck under the couch. Go into the bottom position - with your arms bent, and "push up" with force, using your hamstrings to bring you into an upright position. Lower yourself using your hams for resistance and the spring up again using your arms for assistance. This is a hard one.

Meg