For the Single Leg Raise, lay on your back next to a power rack or door frame. Lock one leg totally out and set it up on the rack/frame so there is just a slight stretch in your hammy. Hands down by your side, palms up, both butt cheeks on the ground, no lock out your down leg – full knee extension – and raise it up as high as possible.
If you have the mobility and can hold your up leg vertical with the knee fully extended, do this rack/frame-free. Just hold your leg up in the air and raise your other.