Clamshell

The clamshell strengthens the muscles at the side and back of the hip, mainly the gluteus medius. These muscles stop the knee falling inwards when you walk, climb stairs or squat, so physiotherapists use the clamshell for knee pain as well as for hip and back problems. It is done lying on your side on a bed or mat and needs no equipment.

Written by Dr. V. B. Rajendra Prasad, MPT, licensed in the US and UK.

1. Lie on your side, hips and knees bent, feet together
2. Keeping the feet together, lift the top knee, then lower slowly

How to do it

  1. 1

    Lie on your side on a bed or mat with your head resting on your lower arm or a pillow. Bend your hips and knees so your heels are in line with your buttocks.

  2. 2

    Stack your hips one on top of the other. Rest your top hand on your top hip to check that it does not roll back.

  3. 3

    Keeping your feet together, slowly lift your top knee as far as you can without the pelvis rolling backwards.

  4. 4

    Hold for 2 to 3 seconds, feeling the muscle at the side and back of the hip working.

  5. 5

    Lower the knee slowly. Do all repetitions, then turn over and do the other side.

How many

10 repetitions on each side, 2 sets, once a day. Build up to 15.

Common mistakes

Rolling the pelvis backwards to lift the knee higher. A smaller lift with the hips stacked works the right muscle.

Letting the feet come apart. Keep the heels touching.

Moving fast. Lift and lower slowly.

Feeling it mostly in the front of the thigh or the lower back. Check that your hips are stacked and lift a little less.

Make it easier

Make the movement smaller, or lie with your back against a wall so the pelvis cannot roll back.

Make it harder

Hold at the top for 5 seconds, or tie a light resistance band around the thighs just above the knees. Standing exercises such as standing hip abduction come next.

Who it helps

Knee pain, especially pain around the kneecap
Hip pain
Lower back pain
Runners and walkers
Weak hips after long hours of sitting

When to stop and check

After hip replacement, ask your surgeon or physiotherapist before doing clamshells, as lying on your side and turning the leg out may be restricted for some weeks. Stop if you feel sharp pain in the hip, groin or back.

Not sure these are the right exercises for you? A physiotherapist can assess you on a video call and build a programme around your problem, guiding each exercise and correcting your form in live sessions.

Get a personal programme

Frequently asked questions

What muscle does the clamshell work?
Mainly the gluteus medius and the small muscles that turn the hip outwards. They sit at the side and back of the hip and keep the pelvis and knee steady when you stand on one leg.
Are clamshells good for knee pain?
They are often part of a knee pain programme, especially for pain around the kneecap, because weak hip muscles can let the knee drift inwards. They are usually combined with thigh strengthening such as sit to stand.

Related

Online physiotherapy: Knee Pain and OsteoarthritisOnline physiotherapy: Back Pain and SciaticaKnee Strengthening Exercises for Pain ReliefKnee Pain When Squatting or Lunging: Causes and How to Train Around ItKnee pain self-check

More hip and buttocks exercises

BridgeSide Lying Leg RaisePiriformis StretchBridge MarchStanding Hip AbductionAll exercises
Dr. Rajendra

Written by Dr. V. B. Rajendra Prasad, MPT. Licensed to practice in the US (NY state) and UK (HCPC).
20 years of clinical experience. About Dr. Rajendra