Let me start by saying that I do not think the side lying clamshell is a bad exercise. I myself prescribe side lying clamshells with specific individuals, but I do have some thoughts on how the exercise is traditionally performed as well as some alternatives that I believe may be more effective.
Let’s give some background before we dive deep into the side lying clamshell. This is one of the most prescribed exercises I have seen in physical therapy clinics and I believe the intentions behind prescribing it are good. Increasing hip abductor strength can be an integral part of a rehabilitation plan. This is because the hip abductors play an important role in keeping the pelvis stable during the single limb stance phase of human locomotion. When the hip abductors are weak we may see compensations occur, such as the knee collapsing into valgus or the low back losing its stability in order to maintain our center of mass over our base of support. The side lying clamshell exercise offers an opportunity to strengthen these important muscles. Like I said, I do not think the clamshell is a bad exercise, but I do think that we forget that progressions exist for this exercise, just like any other exercise. More on that to come.
There will be clients who are appropriate for this exercise, and when we decide to prescribe it, we need to make sure it is being performed properly. Let’s start there.
How to Properly Perform a Side Lying Clamshell
Begin by lying on your side with your hips stacked so they are perpendicular with the floor. Your hips should be slightly flexed and your knees bent to about 90 degrees. Raise your top knee up as high as you can without rotating your pelvis. This is the key component that is often missed. Clients with weak hip abductors will try to cheat by rotating their pelvic posteriorly to achieve their full range of motion. Slowly control the descent back to the starting position.
Using the Hip Abductors as Stabilizers
There are a couple inherent weaknesses to performing the side lying clamshell over other exercises. The first is that the hip abductors are used as prime movers in this exercise, whereas, during human locomotion, the hip abductors function primarily as stabilizers. For this reason, I like to progress out of the side lying clamshell as quickly as possible. The first progression I prescribe is the side plank clamshell. During this exercise, the client assumes a modified side plank position and performs the exact movement as we see in the side lying clamshell. The difference, however, is that during this exercise we are actually focusing on the bottom hip. In the modified side plank position, the hip abductors of the bottom hip must stabilize the pelvis to prevent excessive hip adduction, or lateral pelvic tilt. As the top knee is rotated towards the ceiling, the bottom hip must work even harder to maintain a stable pelvis.
This can be progressed into a full weight bearing position with unilateral abduction. In a similar fashion, the stance leg’s hip abductors must work to maintain a stable pelvis in single limb stance as the opposite leg provides resistance with a mini band.
Truthfully, I’m not even sure it is necessary to program exercises whose sole purpose is to improve hip abductor strength or stability. By performing lower body strengthening exercises in single limb stance, such as lateral step downs or single leg RDLs, the hip abductors are forced to stabilize the pelvis in a similar fashion to what we see during human locomotion. In my experience, this is a sufficient stimulus to improve hip abductor strength and can improve the efficiency of the treatment session when time is a factor.
Pelvis on Femur Rotation
Another weakness of the side lying clamshell is the motion that is occurring at the hip. During human locomotion, the pelvis typically moves on the femur, but during the side lying clamshell the femur is moving on the pelvis. One of my favorite exercises for teaching a client pelvis on femur rotation, as well as how to actively control the amount of hip external and internal rotation they possess, is the T-Hip. Assume a single leg RDL position while holding onto a stable surface for balance. The front knee should not move for the entirety of this exercise. Rotate your pelvis open until you feel a good stretch in your groin. Next, close your pelvis down until you feel a stretch in the hip abductors on your stance leg.
We can progress the T-Hip by using a vasso strap (I have also heard it called a Physical Industries Strap and 3D Strap). The vasso concentrically resists hip external rotation and forces us to eccentrically control hip internal rotation as we return to the starting position. This is similar to the demands placed on the hip during gait.
We can also use a stability bar to progress the T-Hip. This progression requires us to couple concentric hip external rotation with contralateral thoracic rotation as well as eccentric hip internal rotation with ipsilateral thoracic rotation. Once again, this is similar to what we experience during gait.