Cable Kickbacks
When people ask me, "How did you get that hard butt?", I tell them about cable kickbacks and assure them that hard butts do not run in my family! This exercise is performed using the lowest setting of a cable machine attached to leather collars around the ankle. If your gym does not have such collars, an inexpensive substitute is (no kidding) actual dog collars!
Stand with your non-working leg bent slightly (not locked out) and planted about three feet from the cable pulley. Brace your hands on the cable machine's base for support, leaning forward from the hip at about a 60° angle. The starting position of your working leg is with the foot well in front of the stablized foot.
While keeping the knee of the working leg straight, kick your leg straight up behind you. Do NOT twist your torso during the movement: Your hips should remain squared forward for the duration of the exercise, with all movement initiated by the glute (and upper hamstring) of the working leg. An exception of my rule of slow training, this is one exercise where a bit of speed is in order to kick the cable up without straining the lower back.
