I’ve often said that if I were stuck on a desert island and I could only bring one exercise, the humble clamshell would be a strong contender. This exercise is gold for targeting one of the most important and under-utilized muscle groups in our lower body: the deep butt.
The deep butt are six little muscles that run horizontally under the gluteus maximus, connecting the head of the femur to the pelvis at various points and angles. These muscles (the obdurator internus and externus, the gemellus superior and inferior, the quadratus femoris, and the famous piriformis) are external rotators and are vital to stabilizing your pelvis for positions like middle splits and straddles, as well as for life.
But the gold in clamshells is very much in the details. It’s so easy to swish through a set of clams utilizing non-targeted muscle groups like the obliques, the hip flexors, opposite butt muscles, and even the spinal extensors. The gluteal muscles (gluteus maximus, minimus, and medius) are working but not the primary targets here. The first time I figured out how to get all those other helpers to pipe down and really focus on the deep butt muscles I was shocked to find a tiny range of motion and shaking like I was hefting an olympic barbell. But it was just my thigh bone. So exciting!
How to Set Up for Success
Even Out Your Hip Bones: If you have a difference in the diameter of your waist and hips, which most people do, when you lie on your side your top hip will tip up towards your rib cage making your hips uneven. Use your waist muscles to lengthen that top hip out towards your heels until the top hip bone is directly above the bottom hip bone. This will make it harder for your obliques and back muscles to “help out”.
Slight Lean Forward: Very slightly rotate your pelvis forward as if you were considering rolling forward onto your belly. Lengthen your top knee out just past your bottom knee. Feel like that top leg is lengthening out of the hip socket. You are going to maintain this lengthened feeling and forward tilt throughout the exercise to minimize the participation of the gluteus minimus and medius and hip flexors.
Stack the Insteps of your Feet: Make sure that the feet are stacked one directly on top of the other with the insteps lined up and pressed together. That slight press down with the top foot is going to encourage the external rotators to be more enthusiastic.
Tips for Optimal Execution
Nothing Moves but the Knee: Try putting your top hand on your top hip. Don’t let that hip bone move at all. The only movement is the lifting and lowering of the thigh bone.
Bottom Leg Stays Relaxed: It is so tempting to push that bottom leg down to lift the top leg up, and some amount is inevitable. But really try to keep it as relaxed as possible.
Keep it Small: Most of us don’t have a huge range in our external rotation. If you are doing a giant movement where your knee points towards the ceiling every time you are likely bringing pelvic and spinal rotation into it and no longer isolating those deep butt muscles. Keep it small, keep it honest.
Feel the Burn: For most people this is not an isolation we do every day. Those deep butt muscles should be singing! You probably wont need more than 10-20 reps to get to shaky, crampy, maximum. Feel free to do multiple sets but when you get too tired to isolate, take a break.
For you visual learners check out the YouTube video below!
Pro Tip: The standard way to do this exercise is with the hips at about a 45 degree angle and the feet lined up with the hips but that isn’t the only way to do it. You can emphasize different muscles but doing the same set up with the knees tucked up towards the chest or in full extension with the feet back behind me like you were hanging upside down from a trapeze. These exercises are great for improving hip stability at every angle.