The Deep Six Lateral Rotators And Movement
The group of muscles commonly referred to as the deep six lateral rotators of the hip is a fascinating group. But, this may not be a group of muscles that you’ve heard much about. These muscles are an important group for understanding pelvic movement. They contribute to a surprising variety of hip actions. So in this article, we’ll take a closer look at these six muscles and what movements they contribute to.
What muscles are included in this group?
To review, this group of muscles includes:
- Gemellus superior
- Gemellus inferior
- Obturator internus
- Obturator externus
- Quadratus femoris
All of the deep six lateral rotators attach to (originate on) various locations on the ischium of the pelvis with the exception of the piriformis muscle. The piriformis originates on the anterior side of the sacrum. All of the deep six lateral rotators attach to (insert on) various locations of the greater trochanter of the femur at their other end.
How do the deep six lateral rotators contribute to movement?
In my previous article, I discussed some of the specific actions that these muscles do or assist with. And I also mentioned that these muscles are deep to the large gluteus maximus. Their location, deep to a very dense muscle like gluteus maximus, makes it more difficult to determine when the deep six lateral rotators are activated during particular motions with tools like electromyography (EMG).
So, there is still some exploring to do to fully understand the ways that this group of muscles function during different types of activities. Aside from lateral rotation of the thigh, individual researchers and anatomists list different possibilities with respect to which additional actions these six muscles may contribute to.
One thing that it’s important to consider is whether both hips are moving together (bilaterally) or whether we’re describing actions of one hip only (unilateral action). This can change what action these muscles create. When we activate this group of muscles on both sides at the same time (bilateral action), they can contribute to extending the hip joint.
If we were in a position where both legs were free to lift (an open chain position), maybe something like a locust pose in yoga, or alternating prone extensions, then the deep six lateral rotators could contribute to extending our legs at the hip joint. However, if we were standing on both feet (a closed chain position) and bilaterally activated these muscles, then they could contribute to posteriorly tilting the pelvis relative to the legs.
Of course, muscles don’t just initiate action, they also resist opposing muscles and actions. So we could also consider that this group of muscles, acting bilaterally, assists with resisting or opposing all the muscles that flex the hip joint. Myers, 2014 suggests we could even think of these muscles as “extensori coxae brevis,” or the short hip extensors, rather than “lateral rotators.”
If we look at unilateral actions, then we mean that one side of our pelvis is doing something different from the other side. The most straightforward movement that all six of these muscles contribute to is the one they’re named for, lateral rotation. They laterally rotate one leg at the hip joint when you’re standing, but not weight-bearing with that leg.
But how often do we actually stand on one leg and then laterally rotate the other one? This might come up for the dancers reading this, but not so often for the rest of us. What’s more likely is that we all walk. And these muscles contribute to laterally rotating one hip as we take a step (Myers, 2014). But, just like I discussed with respect to the contributions of this muscle group to posterior pelvic tilt, when we change our ideas of origin and insertion, we can see that these muscles as a group could also move the pelvis around the leg.
As I’ve already alluded to, how the deep six lateral muscles act in movement depends on the position of the body. It’s important that we remember that our body is three-dimensional!
For example, Chaitow and DeLany, 2011 refer to a “piriformis paradox.” In open chain, unilateral movement, the piriformis does lateral rotation of the thigh when the hip joint is extended or flexed less than about 60 degrees. But, he suggests that when the hip is flexed more than 60 degrees, piriformis can actually contribute to internal rotation (Chaitow and DeLany, 2011). Similarly, Yoo et al., 2015 and Chaitow and DeLany, 2011 both report that obturator internus, gemellus superior, and gemellus inferior all contribute to abduction of the thigh when the hip is flexed.
While we might have an idea that everything is already known about human anatomy and how our muscles work, this is often far from true. The human body is fascinatingly complex. And, there is a lot we still don’t know about what’s happening with our muscles when we move. Our deep six lateral rotators are one of those groups of muscles that we are learning more about.