📖 Static demo — read-only snapshot
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Clamshell
Positions & Range of Motion
- Start
- sidelying with hips stacked vertically, hips flexed ~45°, knees bent ~90°, feet together, trunk neutral
- End
- top knee rotated open toward the ceiling via hip external rotation while feet stay in contact and the pelvis stays stable (no posterior roll)
- Range of Motion
- hip external rotation, roughly 0 to ~30–45° of knee separation, then controlled return
How to Perform
Sidelying hip external rotation exercise. Patient lies on side with hips and knees bent, feet together, and opens top knee like a clamshell.
Opens a YouTube search for “Clamshell”
Coaching Cues
- 1
Quiet trunk, stacked hips — glute med rotates the femur
(verbal) - 2
Open the top knee toward the ceiling
(verbal) - 3
Keep the feet glued together throughout
(verbal) - 4
Hand on the top hip stops it from rolling backward
(tactile)
Evidence-Based Dosing & EMG Data
3×15-20 reps per side, 2-3x/week
Glute med 26-67% MVIC; highest glute med-to-TFL ratio (115) among exercises [Selkowitz 2013]; 60° hip flexion optimal [Willcox 2013]
Muscles Involved (5)
Primary Movers
Secondary Movers
Synergists & Assistors
Easier Variations ↓
Reduced Range Clamshell
Open the knee only partway. Focus on maintaining pelvic stability.
Harder Variations ↑
Resisted Clamshell
Add a resistance band around the thighs just above the knees.
Elevated Clamshell
Lift feet off the surface while performing the clamshell. Increases gluteus medius demand.
Target Movements (2)
Why This Exercise Matters
Everyday activities this exercise helps you do — essential means it directly trains the capacity the task needs:
Goals This Helps With
Rehab, performance, prevention, and mobility goals this exercise supports — essential means it's a cornerstone:
Evidence Sources (10)
- 📄Therapeutic Exercise: Foundations and Techniques— Kisner C, Colby LA, Borstad J
Therapeutic exercise foundations for Clamshell
- 📄ACSM's Guidelines for Exercise Testing and Prescription— American College of Sports Medicine
ACSM exercise prescription guidelines for Clamshell
- 📄The Non-Surgical Management of Hip & Knee Osteoarthritis (OA) (2020)— Matthew Bair MD MS, John Cody MD, Jess Edison MD, et al.
The Non-Surgical Management of Hip & Knee Osteoarthritis (OA) (2020) — evidence for Clamshell
- 📄Hip Pain and Mobility Deficits-Hip Osteoarthritis: Revision 2017— Cibulka MT, Bloom NJ, Enseki KR, et al.
Hip Pain and Mobility Deficits-Hip Osteoarthritis: Revision 2017 — evidence for Clamshell
- 📄The Influence of Varying Hip Angle and Pelvis Position on Muscle Recruitment Patterns of the Hip Abductor Muscles During the Clam Exercise— Willcox EL, Burden AM
The Influence of Varying Hip Angle and Pelvis Position on Muscle Recruitment Patterns of the Hip Abductor Muscles During the Clam Exercise — evidence for Clamshell
- 📄Comparison of the Effects of 3 Side-Lying Exercises on Electromyographic Activities of Lumbopelvic Muscles in Young Females With Hip Abductor Weakness— Nam SJ, Oh DW
Comparison of the Effects of 3 Side-Lying Exercises on Electromyographic Activities of Lumbopelvic Muscles in Young Females With Hip Abductor Weakness — evidence for Clamshell
- 📄Hip Muscle Activity During 3 Side-Lying Hip-Strengthening Exercises in Distance Runners— McBeth JM, Earl-Boehm JE, Cobb SC, Huddleston WE
Hip Muscle Activity During 3 Side-Lying Hip-Strengthening Exercises in Distance Runners — evidence for Clamshell
- 📄Which Exercises Target the Gluteal Muscles While Minimizing Activation of the Tensor Fascia Lata?— Selkowitz DM, Beneck GJ, Powers CM
Which Exercises Target the Gluteal Muscles While Minimizing Activation of the Tensor Fascia Lata? — evidence for Clamshell
- 📄Examining the Effects of Altering Hip Orientation on Gluteus Medius and Tensor Fascae Latae Interplay— Sidorkewicz N, Cambridge ED, McGill SM
Examining the Effects of Altering Hip Orientation on Gluteus Medius and Tensor Fascae Latae Interplay — evidence for Clamshell
- 📄Superficial and Deep Gluteal Muscle Activation During Common Therapeutic Exercises: A Muscle Functional MRI Analysis— Kim S, Burland JP, Morgan KD, et al.
Superficial and Deep Gluteal Muscle Activation During Common Therapeutic Exercises: A Muscle Functional MRI Analysis — evidence for Clamshell