Clamshell Exercise: Benefits for Hips, Knees and Daily Life
The clamshell is a simple floor exercise where you lie on your side with your knees bent and open your top knee like a clam shell, keeping your feet together. It is a must because it targets the small glute muscles on the side of your hip that keep your knees and pelvis steady when you walk, run and climb stairs.
It looks easy, and that is exactly why people skip it. Done slowly and properly, most of my clients feel it burning within a few reps.
Why the clamshell is a must
The clamshell mainly works the gluteus medius and gluteus minimus, the smaller glute muscles on the outer hip, along with the deep hip rotators. These muscles do not get much attention from big lifts, but they have an important job: holding your pelvis level and stopping your knee from collapsing inwards when you stand on one leg.
The movement is hip external rotation and abduction, turning the thigh outwards and away from the body. Because you are lying down, your body is supported and you can focus on feeling the right muscle work without worrying about balance.
I often use clamshells as part of a warm-up or as an early step for clients whose knees cave in during squats or lunges. They build the base that bigger glute exercises, like the hip thrust, are built on.
How it helps in everyday life
Every step you take is a moment on one leg. Strong side glutes make that moment more stable and efficient:
Walking and climbing stairs with your hips and knees lined up, rather than wobbling side to side.
Standing on one leg to put on trousers, socks or shoes.
Stepping off a kerb or onto a bus without your knee rolling inwards.
Running, hiking and playing sport with better control through the hips.
Standing for long periods, like on a train or at an event, with less hip fatigue.
What it can help prevent
Weak hip muscles are commonly linked with a range of lower body aches. As part of a wider strength routine, clamshells can help reduce the risk of:
Knee pain: when the outer glutes are weak, the knee can drift inwards, which is associated with problems like runner's knee. My post on exercises for runner's knee goes into more detail.
Hip and lower back niggles: a stable pelvis means less unwanted movement through the lower back and hips.
Falls and balance problems: the side glutes are key for staying steady on one leg, which matters more and more as we age.
Muscle imbalances from sitting: long hours at a desk can leave the glutes switched off, and clamshells are an easy way to wake them up.
Who it suits (and who should be careful)
Clamshells suit almost everyone: beginners, runners, older adults, people returning from injury and anyone whose knees cave in when they squat. They are low impact and need no equipment, so you can do them at home.
Be careful if you have had a hip replacement or recent hip surgery, as some side-lying positions and rotations may be restricted for a period. Follow your surgeon's or physio's advice. If the exercise causes sharp pain in the hip or back, stop and get it checked.
How to start safely
Lie on your side with your hips and shoulders stacked, knees bent to about 45 degrees and heels in line with your bottom.
Rest your head on your lower arm and place your top hand on your hip to stop it rolling back.
Keeping your feet together, slowly lift your top knee as far as you can without your pelvis rotating.
Pause for a second at the top, then lower with control.
Start with 2 to 3 sets of 12 to 15 reps on each side.
Easier version: make the movement smaller and focus on just feeling the outer glute switch on.
Harder version: add a mini resistance band just above your knees, or progress to a side plank clamshell. Once you are strong here, the glute bridge is a great next step.
FAQs
What muscles do clamshells work?
Clamshells mainly work the gluteus medius and gluteus minimus on the side of your hip, plus the deep hip rotators. These help keep your pelvis and knees stable.
Are clamshells good for knee pain?
Clamshells are often included in programmes for knee pain because weak side glutes are linked with the knee drifting inwards. They work best as part of a wider plan, so see a GP or physio if your pain persists.
How many clamshells should I do a day?
For most beginners, 2 to 3 sets of 12 to 15 reps on each side, a few times a week, is plenty. Quality matters more than quantity, so keep your hips still.
If you want this coached 1-to-1, my 12-week body transformation in Archway builds exercises like the clamshell into a plan around your body and goals, or see my personal training prices.
