How to Do The Clamshell Exercise With Perfect Form
Don't be fooled; this simple exercise is one of the best for building stronger, healthier hips and protecting the knees.
By Kelan Ern Updated: `05/13/2026
Several years ago, during a personal training session, a client asked me for help with the clamshell exercise: She couldn't feel her glutes working.
Instead she felt a burning on the outside of her thigh... tightening in her calve... or discomfort in her lower back. She knew it wasn't right but didn't know how to fix it.
With a few adjustments (which you'll see in a moment), she instantly felt it in her hips - it was like a whole new exercise.
That's when I told her:
'There are powerful corrective exercises floating around on the internet but people aren't doing them correctly.There are so many distinctions in even simple exercises that if you mess up - you no longer get the benefit.'
In this tutorial, you'll learn:
How to do the clamshell with perfect form
Avoid the #1 mistake
Explore progressions to build stronger, more resilient hips
What Does The Clamshell Exercise Do?
The clamshell is a side-lying exercise that strengthens the glute medius and other hip muscles. It may look boring, but it delivers impressive results by strengthening the glutes, improving knee stability and supporting overall hip health.
Although it looks easy, many personal trainers, group exercise instructors and workout buffs do this exercise incorrectly.
How to Do the Clamshell with Proper Form
Set-Up: Start in a side-lying position with your legs stacked on top of one another. Bend your knees at about a 45 degree angle.
Movement: Keeping your feet together, open your knees without rotating at the spine. Then return to the starting position. You should feel this exercise working the glute muscles. Do 10-15 repetitions each side.
The #1 Clamshell Mistake
The most common mistake during clamshells is an illusive one - even experienced personal trainers miss it. But this little detail makes-or-breaks the exercise. I'll show you how to spot it (and three ways to fix it).
The Mistake: Rotating at the hips and spine.
Look at the picture below:
What's different about it?
At first glance, it looks similar to the previous demonstration.
Look at the height of the knee. Now compare that to the image with proper form.
Notice the knee goes way higher?
That's because to get the knee that high requires rotating the hips and possibly spine with it. This is the most common mistake. And most people don't realize it's happening. Make sure that only your leg is moving.
Not your hips. Not your spine.
Here are three tips for correcting it:
Put your hand on your hip to monitor it for movement (which also helps activate the glutes)
Don't raise the knee as high to avoid rotating the hips and spine.
Put a foam roller standing right behind your hips during the exercise. If you knock it over, you are rotating too much.
Why You Might Not Feel Your Glutes (and How to Fix It)
Maybe you don't feel it in your glutes. Maybe you feel a burning along the outside of your leg (IT band area).
Sometimes it’s because these hip muscles are extremely weak. Or your hip alignment is off, which makes these muscles harder to activate.
Here are a few pro tips to help:
Tip #1: Hand on the glutes Place your hand on your glute when you do the exercise. Believe it or not, when you touch a muscle, it helps activate it.
Tip #2: Bring the legs back Another tip is instead of bending your legs forward at a 45 degree angle, bring them backwards. Meaning: Do the clamshell with your upper legs in-line with your torso.
Tip #3: Pillow underneath you Another way that’s worked for some of my clients is to have a pillow underneath them (right above the hips). This can help put the spine in better alignment – especially for those with larger pelvic bones.
Still Struggling with Glute-Activation? Sometimes the glute bridge is a better place to start for waking up these stubborn muscles.
Clamshell Progressions: How to Make the Exercise More Challenging
After you get the hang of the exercise, here's a little variation to try. In this video by physical therapist Mike Reinold - you'll see him do clamshells with a resistance band around his knees.
This is a sure-fire way to fire up your glutes even more.
Even a small amount of resistance, like those yellow ankle bands from physical therapists, will make this exercise much more difficult.
Remember: Don't rotate from the spine (or the hip). All the motion should come from the leg.
3 Benefits of the Clamshell Exercise
Whether you are doing regular clamshells or band-resisted, you'll get the following benefits with this powerful exercise:
#1: Strengthens Your Glutes When you do clamshells you’re activating your glutes (your butt muscles) which are crucial for walking, running, climbing stairs, picking up objects off the ground or even standing up. When these muscles aren't working properly, the lower back tends to compensate. The clamshell exercise strengthens not just the largest glute muscle (glute maximus) but also a smaller one called the glute medius.
In fact, a 2013study found that the clamshell is one of the best ways to strengthen the glute medius.
#2: Knee Stability In my fitness workshops, I've had audiences try the following exercise:
Stand up and put one hand on your glute (butt muscle)
Gently move your knee side-to-side.
Unless you have a little glute amnesia, you'll feel the muscles in your hip contracting.
That's because muscles like the glute medius help stabilize your knee. Many people want to point their finger at their knee for not being strong enough. But in many cases they should point it at their weak butt (specifically glute medius) that isn't strong enough to control the knee. That's why you see this exercise frequently recommended by physical therapists for knee pain.
#3: Hip Health If you've ever had a massage (or foam rolled) the outside of your thigh (TFL-IT Band), you know how tender and tight this area can get.
When this area gets stiff, it can literally rotate the hips and cause your femur to move improperly in the hip socket - causing hip pain and restricting your movement. However, when you build the glute medius, it helps the femur glide smoothly in the socket. And clamshells do exactly that.
When to Do Clamshells in Your Workout
Clamshells are great at the beginning of a warm-up. Why?
When you activate the glutes (and other important hip muscles) you are more likely to use them during the rest of your workout.
Meaning: your activated glutes will help you when you do squats, deadlifts, lunges, step ups, tire flips or other leg exercises. And ultimately that's going to allow you to get much more out of your workout.
Do 10-12 repetitions on each side.
Do Clamshells Help Knee Pain?
Over the years, one of the most common questions has been:
How do you strengthen the knee?
The problem: it's the wrong suspect.
Many people assume the knee is frequently injured because something is wrong with it. Or it's too weak. But when it comes to the human body.
The symptom of the pain is usually not the source of the pain.
There are exceptions.
For example, if you’re blind-sided by a NFL linebacker, chances are your knee can’t hold up to this force. But outside of collision injuries, we can prevent many types of knee injuries.
And in many cases, the hips are the true culprit.
When the hips are functioning correctly, the knees tend to stay healthy. When the hips are functioning correctly, the low back tends to stay healthy as well. And one of the best ways to keep the hips functioning is with the clamshell exercise.
Final Thoughts
For the last 16+ years of coaching functional movement, certain corrective exercises have come and gone. But the clamshell has been one of the most important exercises in my 'toolbox.' It's one that I come back to again and again.
It's easy to overlook it but it's a powerful injury-preventing exercise. It'll help you move better, positively impact the rest of your workout and help stabilize your knees during your daily activities.
Try them out and see for yourself.
Kelan Ern Elite Fitness Coaching
P.S. There are dozens of other tools and strategies to help you go further, faster on your fitness journey. Each week I share these fitness tips with my 'mind-body community' and do a monthly deep-dive on the fittest people on the planet inside the Mind-Body Breakthroughs newsletter.
