I generally do two types of single leg squats. The first is the one above, the single leg box squat, and the second is the off box squat (no pictured).
Neither of these are should be confused with the pistol squat. Nor do I use these as regressions for teaching the pistol squat. Yes, it is pretty cool when someone can actually go down and hit a pistol squat on cue. But, besides being the only person in a room who can do it, I see no real reward for the risks it poses.
The main difference is two things. First is depth of the squat For the most part, I set up a box where the person can hit parallel. For taller people this may be throwing an Airex pad on top of a bench or box. For shorter people, you can use smaller boxes or have them stand on a 45 or 25lb plate. Going below parallel can cause increased rounding of the back and posterior aspects of the medial meniscus to be pinched or compressed in the joint line. There's also no real added benefit of hitting below parallel unless you sit in children's furniture...with one leg (which i actually do sometimes but only with two legs :/).
The second difference is the up leg position. During the single leg box squat, the up leg heel stays slightly off of the ground. The leg can either be straight or slightly bent. In a pistol, the up leg is sticking straight out. This adds increased stress on the hip flexors and could result in back pain. Clients with longer legs are at greater risk. These longer levers create even more stress on the back. Once again, no real added benefit unless you're deep squatting in a puddle and don't want to get the other foot wet.
So when executing the single leg box squat (with body weight only) focus on the following:
- Set up with your arms out, off leg slightly bent with heel off the floor.
- Lower yourself to the box in control. No falling or "plopping" on to the box
- Try to barely touch the box before you return. I tell my clients, "act like there is a tack on the box." (However, if you are new to this exercise you can sit all the way down if you are not strong enough to touch and go).
- Upon returning to the standing position maintain good posture and push through your heel. You can brace your core to help maintain posture and keep from going into hip flexion as you stand.