The Single Leg Hip Hinge is my favorite for building hip muscles (hamstrings and butt) while minimizing wear and tear on the knees and spine. The Single Leg Hip Hinge is a great combination of strength, balance, and keeps us protecting our spines. Single Leg Hip Hinges can be modified in a variety of ways to suit nearly anyone. 
You can easily challenge several variables – the range of motion, the overall load you are moving, and your sense of balance. Performing the exercise on 2 legs will generally be easier than 1 leg. However, as shown in this Single Leg Hip Hinge demonstration video, we can use support for balance.
The most important part of the exercise is using your hip muscles rather than your back muscles. You can accomplish this by reaching across you body while performing the exercise. So, if you are using your left leg, reach across with your right arm. This helps shift your body weight onto your left leg. 
One common question that comes up is the position or shape of the spine. If you are attempting to perform a spine sparing exercise, shouldn’t you avoid bending it? Performed correctly, the Single Leg Hip Hinge will focus the bending at the hip with good core muscle stabilization of the spine so the spine just “comes along for the ride” as the hips do all the work. This is a concept we will keep returning to. If we can sense our side abdominal muscles, we can reasonably assume that our spine, ribs, and pelvis are playing together nicely, creating overall stability of the spine throughout this hip focused movement.
